The Alaska Department of Fish and Game is preparing to move forward in the second phase of a project to eradicate the invasive northern pike from Kenai Peninsula waters, specifically the Soldotna Creek mainstem.
Rob Massengill, a fisheries biologist with Fish and Game in Soldotna, presented an update and timeline of the department’s treatment plan to the Soldotna City Council at its Wednesday meeting.
Though northern pike are not invasive in all areas of the state, Massengill said they are largely not native south of the Alaska Range and are believed to have been illegally introduced sometime in the 1970s. Fish and Game treated several lakes in the Soldotna Creek drainage with a piscicide called rotenone in 2014. So far, Massengill said the eradication appears to be successful, with no pike having been discovered in the lakes since.
“We went in and netted it and tested for pike DNA a half a year later after ice-out and we did not detect any pike,” he said. “Pike aren’t able to get back in because we have a series of fish barriers preventing them from moving from Soldotna Creek back into that system.”
Now Fish and Game plans to target the Soldotna Creek mainstem starting this June with the second of two grants it received from the Alaska Sustainable Salmon Fund to eradicate the pike.
“It’s really deadly on fish because the compound’s easily absorbed through gills, so if you’re a gilled organism, you’re in trouble,” Massengill said. “A lot of people think rotenone removes the oxygen from the water, but it doesn’t. What it does is prevent the organism from using the oxygen that’s in their blood at the cellular level.”
Staff will use portable drip stations and backpack sprayers to inject the compound into Soldotna Creek, according to a notice from Fish and Game published in December 2015. Some submerged wetlands near Sevena Lake and some sloughs along the creek corridor will require treatment via helicopter, according to the notice.
To ensure the pike problem is really taken care of, Fish and Game will repeat the treatment again in 2017, Massengill told the city council. Both cycles of treatment should only take about five days, with employees treating two to three miles each day.
Council member Paul Whitney expressed concern about the safety of wildlife near the creek, asking what would happen if animals ate dead fish that had been in the rotenone-treated water.
“It’s not harmful to birds, mammals, people (or) plants at the concentrations we use for fishing management, which is around 40-50 parts per billion,” Massengill said.
Homeowners along Soldotna Creek will not be affected by the treatment other than Fish and Game staff needing to access the water from their property. Massengill said roughly 80 property owners have already been contacted, and most have agreed to let department staff use their property during treatment. Some are still weighing the decision, but so far no one has declined, he said.
“We’ve had overwhelming support,” he said.
At Wednesday’s city council meeting, Massengill headed off concerns about what would happen to fish in the Kenai River if the rotenone exited Soldotna Creek by explaining that the compound has a very short life in warm water, degrading on its own within two to four weeks. Since both treatment phases are slated to take place during summer months, the rotenone is expected to be so diluted by the time it reaches the Kenai River that it will no longer be harmful to fish.
Just in case, though, Fish and Game will use potassium permanganate, an oxidizing agent, to neutralize the rotenone before it reaches the river, Massengill said.
“It’s a common chemical used in … city water systems to clean up water,” he said. “The downside is it can stain the creek purple temporarily, so Soldotna Creek near the mouth might have a purple color to it but it’ll quickly dilute in the Kenai (River).”
The only creatures likely to be negatively affected by the project are aquatic invertebrate called zooplankton, which Massengill said are a food source for small fish and have been known to decline heavily when exposed to rotenone. They take between one and three years to bounce back, but it won’t pose a problem for any of the fish that feed on them, he said.
Signs explaining the presence of the rotenone and listing contact information for Fish and Game will be placed around the treatment area for residents, Massengill told the council. Fish and Game won’t remove them until they are able to test the creek water and determine all of the rotenone is gone, he said.
About 30,000 native fish have already been taken from Soldotna Creek in preparation for the eradication, and Massengill said Fish and Game will begin removing more this spring, most likely starting in early May. They will be placed either in the newly pike-free lakes in the drainage or in the Kenai River until the project is finished, he said.
Massengill emphasized that the community is very lucky northern pike didn’t migrate to the Moose River, which boasts the kind of habitat they tend to thrive in, before Fish and Game got to them in the Soldotna Creek drainage. The project is all about preserving the area’s native fisheries, which have already been negatively impacted by the pike, he said. Having evolved for thousands of years without any other major predator in a habitat that overlaps with that of the northern pike, rearing rainbows and salmon are easily exploited if no intervention is made, Massengill said.
Reach Megan Pacer at firstname.lastname@example.org.