Need to net
Game and Fish discuss solutions for Flaming Gorge fishery
November 2, 2023
When it comes to the issue of declining rates of kokanee salmon in the Flaming Gorge, the Wyoming Game and Fish Department is having conversations with the public about the problem and considering more drastic solutions, such as netting small lake trout on a large scale.
The WGFD's Green River Region hosted a public house meeting at the Green River campus of Western Wyoming Community College on October 18 to discuss the Flaming Gorge fishery. Green River Fisheries Biologist John Walrath gave a 45-minute presentation to share data on the fish in the Gorge, and he and Regional Fishery Supervisor Robert Keith spent nearly an hour and a half answering questions from the over 50 local anglers and concerned citizens in attendance.
"Flaming Gorge Reservoir is a popular destination fishery," Walrath said. "It attracts anglers from all over the US. It's over 90 miles long. And due to this length there's a lot of changes that happen in the reservoir."
Walrath went over data regarding the fish in the Gorge, which include rainbow trout, brown trout, cutthroat trout, smallmouth bass, illegally-introduced burbot, and kokanee salmon. Many fish are stocked in the reservoir every year, including a stocking objective of 700,000 trout and 1.65 million three-inch kokanee, according to Walrath.
Kokanee salmon were first stocked in the Gorge during the 1960s and they established a natural spawning population. Walrath explained. At the beginning of the 1990s, a supplemental stocking program for kokanee was established because the lake trout diet shifted to kokanee in the 1980s, leading to a decline in the kokanee population.
Although the Game and Fish department has been meeting the stocking objective in recent years, data shows an increase in the decline of kokanee in the Gorge, as well as a lower survival rate of kokanee ages zero to two years, Walrath said. Other fish species have also seen declining numbers in recent years.
"It's our concern that the declines in the kokanee, rainbow and cutthroat population is the result of lake trout predation," Walrath explained.
When discussing lake trout, the Game and Fish makes a distinction between small lake trout, which are smaller than 28 inches, and trophy lake trout, which are greater than 28 inches. Walrath explained the Gorge has also seen a decline in the trophy lake trout population and an increase in small lake trout. He noted this could be the result of trophy lake trout having less prey available, such as kokanee salmon. However, he added that "lake trout have evolved to survive in unproductive systems and they don't readily die from starvation."
There have also been studies to look at lake trout age and growth, as well as factors like diet.
"The data is suggesting that there are two different growth trajectories," Walrath explained. "There are individuals in the population that have a much higher growth potential and another that maxes out around 23 inches."
When considering lake trout diet, a study showed that kokanee salmon make up roughly 15% of the diet of small lake trout less than 17 inches.
"This information alone is quite alarming," Walrath said. "When you couple this data along with the length frequency histogram, these size classes of lake trout are the majority of the lake trout swimming around, and kokanee are making up over a quarter of their diet. So this means that too many of these lake trout could have a large impact on other sport fisheries."
Part of understanding the impact of lake trout on other fisheries is understanding how many lake trout are in the Gorge, which is why Game and Fish did a population estimate for lake trout this year. They also tried to break it down into size groups, since estimates done in the 1980s were for the population as a whole.
"We generated a population estimate of around 43,000 lake trout less than 25 inches," Walrath explained. Considering the amount of lake trout as a whole, "the estimate we got is roughly three times higher than the estimates completed in the 1980s."
The Game and Fish isn't done with their studies, either. They are working on bioenergetic modeling as well as spawning and yield modeling in order to better understand the size of lake trout with the greatest impact on sport fisheries and better determine how to sustain a healthy balance of sport fishes and trophy lake trout.
Another new type of research the Game and Fish is working on is genetics work, Walrath explained. They hope to determine whether there are two distinct lineages of lake trout in the Gorge, with one that can grow to be trophy size and one that stays below 23 inches. If they can prove there are two different groups, they can begin working on differentiating them and finding ways to target the smaller group.
The Game and Fish Green River Region is hoping to have their next studies completed by winter of 2024.
"The lake trout problem isn't new," Walrath added, noting that many actions have already been taken, and without those actions the current problem could have occurred much sooner.
Actions that have already taken place include annual gill-netting in the spring, which helps with studies, and an increase on the limit of lake trout that can be caught, which is currently at 12 fish per day.
Walrath also addressed potential solutions that have been offered by the public, and reasons those solutions may not help. Using a barge to stock fish away from boat ramps has been done in the past, but was abandoned due to safety concerns, and purchasing a new barge would be expensive. Stocking at night to decrease bird predation might help initial numbers, but bird predation is a constant that hasn't affected the fish population significantly in the past. Increasing stocking rates would be difficult since Game and Fish facilities are already at capacity and it could simply exacerbate or mask the true issue. Stocking another forage fish would likely cause competition for food sources and could negatively affect the kokanee population further.
When it comes to both decreasing the limit on kokanee and increasing the limit on lake trout, these actions can have marginal gains but don't address the main issue of predation and aren't enough to significantly impact the lake trout population or return the kokanee population to its prior density.
"It's becoming clear that anglers alone might not be able to decrease the [small lake trout] population enough and that additional actions such as targeted netting may be necessary," Walrath explained. "Going with this action will likely result in the slow recovery of the kokanee population. Reducing lake trout population has shown the recovery of kokanee populations in other waters in the US already."
During the question and answer portion of the meeting, much of the discussion revolved around the impact of fishing regulations and the possibility of actions including allowing the harvesting of an unlimited number of small lake trout, removing the wanton waste law for small lake trout, and doing large-scale netting.
Regional Fishery Supervisor Robert Keith explained that one of the biggest issues is simply getting the public on board with understanding the problem and supporting the need to significantly reduce the small lake trout population.
"We need the angling public that love that reservoir to get on board with that solution," Keith said. "We don't like it, but it has to happen. We don't get any pleasure out of going and killing fish just because we need to remove them. But to get this fishery back, they've got to go. Unlimited harvest - that's a tool. Net removal - that's really where we need to go."