Efforts to keep northern pike in Stormy Lake out of the Swanson River watershed culminated last week in a multi-agency effort to treat the entire lake with the fish-killing poison rotenone.
Alaska Department of Fish and Game biologists, along with Fish and Wildlife personnel, closed Stormy Lake the weekend before Labor Day to complete a multi-year rescue of the remaining native fish before treating the lake for its more than decade-long northern pike infestation.
Robert Begich, area biologist with Fish and Game, said multiple agencies, including the Department of Natural Resources and the Kenai River Sportfishing Association, contributed to the project.
On Wednesday, as boats canvassed the lake working their way in slow circles, pushing fish toward the middle of the lake, workers in gas masks mixed powdered rotenone with lake water before applying it to the surface.
Begich said there were close to 30 people on the lake at any given time.
Several canvassed the weedy shorelines with backpacks of the poison, while another boat injected it into the deep waters of the lake.
Stormy Lake is set to reopen Monday and Begich said a potassium drip station, which neutralizes the poison, had been applied above the outlet to the Swanson River overnight.
Rotenone is a broad-spectrum piscicide, or fish killer,
It is lethal to fish because it blocks their ability to use oxygen in their bloodstream, according to Fish and Game.
Rotenone has been used effectively to treat Arc Lake and Scout Lake, Begich said.
Stormy Lake is by far the largest lake on the Kenai Peninsula that has been treated and Begich said it may be one of the biggest in Alaska.
The lake is located in the Captain Cook State Recreation Area, and before the introduction of northern pike it contained a populations of arctic char, rainbow trout, coho salmon and stickleback.
After nearly a decade of pike predation, Begich said the fishery was almost demolished.
The department did an egg-take on arctic char. Those hatchery-raised fish will be returned to the system, and coho salmon may be able to naturally repopulate the lake from the Swanson River system, Begich said.
There are, however, very few fish left in a the lake. Pike are known to demolish fisheries to the point that they limit their own food options, according to Fish and Game.
The department chartered a purse seiner, or drag net, to sweep the lake as part of its rescue operation.
“It didn’t catch anything,” Begich said. “It was bad.”
The arctic char in Stormy Lake are genetically distinct from other char populations in the Swanson River watershed, and Begich said it was a priority for the department to save it because they couldn’t be found elsewhere.
The Swanson River drainage contains 240 square miles of interconnected lakes that provide a vitally important salmon habitat, Begich said.
According to Fish and Game, pike are found in more than 130 lakes and streams in the Cook Inlet Region, with 13 of those water bodies inside the Kenai Peninsula Management Area.
Since being introduced in the Susitna River drainage pike have damaged the coho, king and sockeye populations, according to the Southcentral Alaska Northern Pike Control Committee.
According to researchers for Fish and Game, northern pike in the Swanson River drainage could spread to other drainages including Moose River, which is one of the main spawning and rearing grounds for coho salmon in the Kenai River drainage.
Other efforts to combat pike encroachment on the Kenai Peninsula were tested with varying success on Derks Lake, an isolated water body near Mackey Lake in Soldotna.
Fish and Game teamed up with the United States Geological Survey to test a “water cannon” which Pat Shields, area biologist with Fish and Game, described as a “big squirt gun.”
The department tested two sizes of cannons and while the tests are ongoing, Shields said researchers had drawn a few conclusions about how pike were affected by the shockwaves of water generated by the cannon.
This was the second year of testing for the water cannon, Shields said researchers wanted to know if they could kill pike outright, among other things.
“We didn’t find any or very few pike that it would outright kill,” Shields said. “ Some people thought, ‘You’re not even going to find anything. There’s just going to be pieces of them,’ and that wasn’t true.”
While researchers didn’t see any immediate fish mortality from the trauma of the water cannon, Shields said the pike showed signs of internal damage.
“When you cut it open and then you pull their entrails out — their guts out — and then there’s this bloodline that’s up on their backbone … that’s their kidney,” Shields said. “When you would open these pike up … you’d look at that kidney and there’d be chunks of it missing.”
Researchers will continue to conduct tests with the water cannons to determine how to most effectively use them, Shields said, though they did not prove to be a singular method to control pike predation.
“The whole purpose of this project was to test this as a tool as a method of pike suppression,” he said.
USGS also teamed up with the Cook Inlet Aquaculture Association to experiment with pike in Derks Lake.
Matt Smukall, project technician with CIAA, said the two groups were trying to test the effectiveness of an electric barrier, or Neptune, that could potentially be used to block fish from swimming into a certain area.
Smukall said the team had trouble getting the test fish to stay in the large net, and the group would reconfigure the experiment to try in another lake.
“We have data from other experiments … that proves that the electric barrier works on fish, the main question is if it works on pike,” he said.
That project is in the first year of a three-year grant paid for by the Alaska Sustainable Salmon Fund, and CIAA is using a portion of that funding to conduct pike tracking experiments in the Susitna watershed in the northern part of Cook Inlet.
Begich said Stormy Lake was “on the fast track” for having its fishery restored and biologists are hoping that they will be able to keep pike out of the Swanson River drainage.
“People should know to be patient,” he said. “The fishery will come back. We’ll have to regulate the char and rainbow fishery. But it will be back.”
As he left for the weekend after finishing the remaining few days of treatment, Begich said the feeling of relief was almost overwhelming.
“I’m still trying to get my head around it — that the pike are dead now — it’s just a really good thing,” he said. “It’s a really big step. Just having the threat of the spread minimized now at the Swanson River drainage is really something.”
Rashah McChesney can be reached at firstname.lastname@example.org.