Non-native trout may face chopping block
By Marit Gookin
When Game and Fish Fisheries Biologist Paul Gerrity delivered his annual “State of the Fisheries” talk at Wildlife on Tap on Tuesday, he had some exciting news for the room: Game and Fish is looking into reintroducing a population of Yellowstone cutthroat trout near Lander. However, this measure may require removing a population of brook trout that currently occupy Sawmill Creek.
Cutthroat trout are the only species of trout that are native to Wyoming, and of the four subspecies within the state, only one – Yellowstone cutthroat trout – are native to the Lander area. Introduced species such as brook and rainbow trout have had a severe impact on cutthroat trout populations, as they often out-compete them for the same resources. Although conservation efforts have managed to re-establish a few stable populations of Yellowstone cutthroat trout, according to Gerrity, they still only occupy less than half of their historical range.
“They’re considered a sensitive species – a species of greatest conservation need,” explained Fisheries Biologist Joe Deromedi. “That’s why we worked to restore, or to expand, their habitat.”
There are several populations of Yellowstone cutthroat trout that are doing well near Dubois, but there are currently few near Lander, and Game and Fish is looking to expand their range. However, finding habitat that is appropriate to reintroduce them into can be difficult. Since they can’t compete with introduced non-native trout species, Game and Fish needs to carefully locate isolated drainages with natural barriers that will prevent other trout species from coming back up into the stream; there’s no point in introducing the Yellowstone cutthroat trout to a lake or stream if the population is only going to immediately plummet due to the presence of non-native species, after all.
Once such a drainage has been found – in this case, Lander’s Sawmill Creek – Game and Fish officials evaluate it over the course of several years to see if what they think may be a barrier remains one throughout different water levels. Flooding in particular can cause what is normally a barrier that would prevent fish from going further upstream, such as a waterfall, to become traversable.
If all goes well throughout this evaluation period, in areas such as Sawmill Creek there is one last hurdle to be overcome before the Yellowstone cutthroat trout can be stocked in the drainage: The introduced trout species, in this case brook trout, that are currently occupying the stream. One of the options Game and Fish has used in the past for solving this problem in other areas of Wyoming is a treatment called rotenone. Derived from the root of a South American plant, rotenone kills “anything with gills,” according to Gerrity, but is generally harmless to other animals. It degrades quickly, usually within 24-48 hours depending on factors such as water temperature, and Game and Fish adds potassium permanganate into the stream below the area it is treating with the rotenone in order to neutralize it.
“Our rotenone treatments are done cautiously, and with a lot of oversight,” said Deromedi.
Using a treatment such as rotenone isn’t something that Game and Fish can just do on a whim, and requires extensive consultation with other agencies such as the Forest Service, the Environmental Protection Agency, and the Department of Environmental Quality – and, of course, with the public. Treatments such as rotenone can be controversial, and Deromedi cautioned that it will still be years before the Game and Fish would potentially use the treatment – although they plan to begin having conversations this winter with the public and other agencies about whether it would be an appropriate step to take for Sawmill Creek.
“We’re still kind of in the evaluation phase,” Deromedi clarified. “It’ll take about three years to collect all that data [and] collaborate with other agencies … Treatment may be in August 2025 or 2026.”
While one person present at Gerrity’s “State of the Fisheries” talk questioned the necessity of killing off brook trout in order to introduce Yellowstone cutthroat trout, describing it as “extreme,” most of the room seemed to feel fairly positive.
“This is a rare spot to find and to have, and to maybe undo some of the bad choices we made a while ago,” said one of the anglers in response.
For now, Game and Fish is hoping to start raising public awareness about Yellowstone cutthroat trout and the relatively unique possibility that Sawmill Creek may present. And at least some of Lander’s fishing community is apparently already fully onboard with the idea of helping to revitalize Wyoming’s native cutthroat trout population.