By Lew Freedman
Via Wyoming News Exchange
CODY — The long-running, ongoing battle against invasive lake trout in Yellowstone Lake is turning in favor of the native cutthroat trout.
Deploying an arsenal of weapons to tamp down lake trout reproduction and eliminate older fish, the National Park Service reads optimism into recent trends that show a decline in the number of larger predators who otherwise would devour the cutthroat.
The $2 million-per-year, labor-intensive effort continues in 2019 because while the park service claims skirmish victories, any letup could still alter the big picture.
“It’s not to say we won the war,” said park service fisheries biologist Pat Bigelow at a meeting Tuesday night at the Cody Hotel.
The monitoring of the lake trout situation in Yellowstone Lake was a major topic when the park service held its annual Cody fisheries discussion visit before about 35 people.
This is the most high-profile invasive species issue inside 2.2-million-acre Yellowstone National Park that is the oldest in the country and a high-priority for preserving and restoring the lead species in the 136-square-mile lake with 110 miles of shoreline.
The park service has attacked the problem like an army, constantly introducing new weapons into the fight.
While this has led to more than three million lake trout being removed from the water, it is estimated because of reproduction, more than 600,000 remain. However, that is a huge reduction from the estimated 900,000 lake trout acknowledged in 2012. Also, the recent downward trend has been notable.
Bigelow said between 2017 and 2018 a 25 percent drop was recorded. There were 400,000 lake trout removed from Yellowstone Lake in 2017 and 297,000 in 2018. It was not for lack of trying, but because it is believed the overall numbers are down.
“It’s been really encouraging these last few years to see this decline,” Bigelow said.
Not only is it expensive, with about half the $2 million cost funded by Park fees and the other $1 million contributed by Yellowstone Forever, but park service personnel are forever entertaining more creative and efficient options to eradicate the lake trout.
By now park service workers are trained assassins when it comes to fish kills. The most obvious and widespread venture is built around gill-netting, with four boats from contractors and two Park-operated boats prowling the waters from spring to fall.
Over recent years, the park service has supplemented gill-netting assaults on the lake trout with electroshocking, suction dredging and suffocating eggs on spawning beds by dropping the gill-net to captur fish carcasses on top.
That approach was successful, but the dead fish introduced a new problem.
“It was a grizzly bear attractant,” Bigelow said.
The bears viewed the easy-to-grab fish near shoreline as a free dinner.
To counteract that, the park service shredded the carcasses and used them in the same manner.
“Grinding up the fish worked really well, too,” Bigelow said.
And the bears did not come around to nibble.
There have been laboratory experiments with chemical treatments, or poisons, but the park service has not tried that method yet, hesitant “because we don’t have the delivery system,” said Todd Koel, Park fisheries supervisor.
Also in the mix are analog pellets that are plant-based and do not attract bears. They are seen as holding significant potential to reduce the lake trout population.
“It really, really, really works well,” Koel said.
Since they were first discovered in Yellowstone Lake in 2002, there has been much speculation about how lake trout invaded. It is generally suggested it was a deliberate act of sabotage by humans, perhaps by shifting lake trout from Lewis Lake.
Recently, Koel developed a new theory of how this problem began. After studying fish movement in the Flathead River system in Montana that resulted in invasive species near Glacier National Park, he wonders if that could have happened with Yellowstone Lake.
“They naturally invaded,” he said of the Montana situation.
Koel said what really happened at Yellowstone Lake will remain an unknown and the basic premise that the lake trout were purposely introduced remains valid.
“It could easily have been hauled by buckets,” he said. “It would have taken a lot of buckets.”