Editor's Note April 21: This story has been updated to correct a misuse of the word "invasive." In this case, burbot are not classified as invasive, but are also not native to the area that was being treated in this project. That makes them "nonnative." The article has also been updated to clarify some details of the project. and clarify some aspects of the project.
Last month, the Wyoming Game and Fish Department (WGFD) celebrated a rebound of native fish in the Big Sandy water basin after 20 years of planning and treatment.
The project aimed to restore populations of flannelmouth suckers and bluehead suckers, which are listed as species of greatest conservation need in Wyoming and the Colorado River Basin.
“The flannelmouth and other native suckers are large river species. They used to swim the entire Colorado Basin and spawn in the smaller systems like Big Sandy,” said John Walrath, a fisheries biologist who worked on the project. “But the dams cut off the ability to enter places to spawn.”
He added that when the dams were built in the 1960s, they trapped some of the large river species that were upstream from returning to the Colorado River. As most Colorado River tributaries were dammed, these species struggled to reproduce, which resulted in declining populations throughout their native distribution.
“But we still have remnant populations in Wyoming. They're all the way in Colorado, Utah, New Mexico – the whole Colorado River Basin,” said Walrath.
At the same time, there was an increase in nonnative fish competing for resources.
This project focused on removing illegally introduced burbot, which were eating the smaller native suckers, and nonnative suckers, which were hybridizing with the native suckers.
A 2002 to 2006 assessment in the Green River drainage identified four main watersheds that needed conservation work to preserve native fish. The Big Sandy was one of the largest of the proposed projects: a 52-mile stretch of river and the reservoir it feeds into.
“ Wyoming is one of those states that will take a portion of their budgets and personnel time and is happy to do native fish work or non-game species work,” Walrath said.
Before starting, the department needed to discuss options with private landowners along the river to let them treat it. Landowners, who could charge anglers to fish their stretch of the river, were concerned about how the treatments might affect the catch. So the department and the landowners compromised that the project would start with low-impact treatments that wouldn’t remove any sport fish, like trout.
“It wasn't possible without landowner buy-in. If any one of them had said, ‘No, we don't want to see this happen,’ then the project couldn't have happened,” Walrath said. “It's a lot of kudos to the landowners for agreeing to this type of project.”
Initially, the area was going to be broken into bite-sized portions for treatment. WGFD installed a temporary barrier to isolate the fish and treat each system individually. But spring snowmelt overpowered the barrier, so the department decided to treat the whole basin at once instead.
In 2009, it started the first treatment of the whole basin. Using electricity to stun the fish, they picked out the nonnative species while leaving the native species in the river. They successfully removed 2,600 nonnative suckers.
But nonnative species populations continued to rebound.
The department had previously pitched the landowners on chemical treatment, using a toxin called Rotenone to kill off the nonnative fish. Initially, the landowners pushed back, as they were concerned about how it would affect the sport fish that would stay in the river, like trout. But they eventually changed their minds.
“In 2020, the landowners themselves started to be more accepting of the idea of a longer-lasting removal of the burbot,” said Walrath. “They were catching more burbot and fewer trout, and there were noticeable increases in the nonnative suckers.”
The numerous nonnative fish were using resources that the local population of native fish could have been using. Seeing this in action finally tipped the scales in Rotenone’s favor.
Before releasing the chemicals, WGFD salvaged as many of the bluehead and flannelmouth suckers and trout from the river as possible and trucked them to holding facilities. Sport fish like trout were also moved but stayed within the basin upstream to an area separated from where the treatment was going to be by a temporary barrier. Once the chemical degraded, the sport fish were moved back.
From 2022 to 2024, 2,100 native suckers were released into the river.
WGFD sampled the area in 2024 to evaluate the recovery of the native fish and check for any nonnative species that may have made it through the treatments.
That first evaluation showed promising results that the river's treatment was a success. However, when they sampled the Big Sandy Reservoir, there were still some unwanted fish that had made it through the treatment.
“ We missed a few of the itty bitty fish, but it's still been pretty awesome to see people out there this winter catching, like, 23, 24-inch rainbows,” said Walrath. “Whereas before, they were always complaining that they were only catching suckers, burbot or really small sport fish. It's been awesome to see that fishery turn around.”
A barrier will remain between the river and the reservoir so that those unwanted fish don't travel upstream.
While the bulk of the Big Sandy project is done, Walrath still plans to restore some of the habitat for the suckers. He wants to plant willows and cottonwoods, both for shade – where suckers prefer to reside – and to reduce erosion.
“I think what we've demonstrated is that when we can get the resources and everyone is working together, we can get some of these big legacy-type projects completed, which will have the greatest impact on our conservation efforts,” Walrath said.
The department has just a few years left in its treatment of the Muddy Creek Basin, which is south of Rawlins, and plans to work on the other two areas identified in the 2002 assessment. According to Walrath, those projects will be similar.
