We had been here before.

Agencies, nongovernment organizations and community members had all taken part in an effort to remove invasive northern pike and elodea because we believed that they threatened salmon and other native fish that we value.

Beginning in 2018 and going into 2019, after years of cooperation and labor, we had gotten rid of all known populations of these two top-priority aquatic invasive species on the Kenai Peninsula.

This changed when a member of the public reported a northern pike from remote Vogel Lake at the north end of the Kenai Peninsula. The Alaska Department of Fish and Game followed up, surveying Vogel Lake and connected lakes for northern pike. They also discovered a population of elodea.

Eradication efforts followed over the next two years, removing both species from the area by 2022. It was good that these populations were found early before they had made it far into connected lakes and streams.

Coming into the 2023 field season, it was a déjà vu situation. All known populations of northern pike and elodea were again gone.

No one expected this situation to last indefinitely. Given that northern pike and elodea had made it to the Kenai Peninsula multiple times in the past, there was a good chance that they would show up again sometime, somewhere.

Our best strategy at this point was to look for new infestations as early as possible before they had the chance to spread. Surveying for elodea and pike is no small task, with over a thousand lakes on the Kenai Peninsula.

In the 2023 field season, the Kenai National Wildlife Refuge fielded a crew dedicated to seeking out aquatic invasive species, largely thanks to National Wildlife Refuge System Strike Team funds. Biological Technicians Nathan Davis and Kristian Merrell, with interns, volunteers and others, spent much of their summer driving, portaging, paddling and flying out to lakes all over the Kenai National Wildlife Refuge.

Narrowing down the thousands of lakes to something achievable, the biology team prioritized lakes where northern pike and elodea would most likely show up. We also added a few lakes to the list where we needed more information.

We focused on northern pike in May and June, using syringes to filter 119 water samples from 16 lakes. (There had been 120 samples, but we dropped one into a lake.) We shipped the samples out for environmental DNA (eDNA) analysis to determine the presence of northern pike DNA in the water.

The lab used two kinds of assays: Two-thirds of the samples they tested only for the presence of northern pike DNA; the remaining one-third of samples were analyzed using more expensive metabarcoding methods, which could potentially detect all fish species.

Our choice of methods was a compromise between our priority of detecting northern pike and a chance of detecting any non-native fish species that might be out there.

After all, other non-native fish, including yellow perch, muskellunge, fathead minnow and Alaska blackfish have been introduced into Kenai Peninsula fresh waters in the past. All except the Alaska blackfish were subsequently eradicated.

Over the rest of the summer and into the fall, we looked for elodea using throw rakes, the current state of the art for detecting this plant. Elodea does not shed much DNA into the water, making eDNA methods ineffective for detecting it.

We made throw rakes from two heads of garden rakes welded back-to-back. A D-ring was welded to this and attached to a length of chain and 30 feet of rope.

We worked from a canoe or packraft, typically positioned in the shallows near shore, where elodea is most likely to be present. One person threw a rake toward shore, and the other person threw a rake out toward the center of the lake. We pulled in the rakes simultaneously, dragging them along the bottom.

We then lifted the rakes into the boat and examined what they dragged up. This method works well for seeing what plants are on the bottom of a lake. It is also quite messy, splattering muck and plant bits all over the bottom of the boat.

Our aquatic invasives team surveyed 23 lakes for elodea, checking at 476 locations for a total of 952 rake throws. Thankfully, we found no elodea. We also detected no northern pike in our eDNA samples.

We did find one thing we did not expect, though.

In an unnamed lake one mile east of Big Merganser Lake off Swan Lake Road, where we had yet to find any previous records of fish, the metabarcoding data showed one detection of arctic char DNA. This species interests us because it can be particularly vulnerable to changes, including the potential establishment of invasive northern pike on the Kenai.

That single detection of char DNA could have been erroneous, so several of us returned to that lake on a frosty September morning to check for char using rod and reel.

Not long after setting our canoes in the water from which a morning mist rose, schools of sticklebacks disturbed the glassy surface, followed by ripples from larger fish. That day, we landed multiple char in not one but two adjacent lakes, adding to the list of known char lakes on the Kenai. That was my favorite field day of the field season.

The refuge’s team was one of several teams doing similar work this season. The Alaska Department of Fish and Game, Chugach National Forest, Kenai Watershed Forum and the Homer Soil and Water Conservation District also surveyed for freshwater aquatic invasive species on the Kenai.

The bad news from these efforts is that elodea is now present in Crescent Lake, which fits a quote of Yogi Berra, “It’s like déjà vu all over again.”

The good news is that a crew from Chugach National Forest discovered this population early, validating why we all have been out searching for aquatic invasive species — so that we can take action to protect salmon and other native fish that matter to us.

Unlike when elodea was first found on the Kenai in 2012, we now have plenty of experience dealing with it and a reasonable hope of success in eradicating it based on that experience.

Matt Bowser serves as a Fish and Wildlife Biologist at Kenai National Wildlife Refuge. Find more Refuge Notebook articles (1999–present) at https://www.fws.gov/kenai-refuge-notebook.

Friends of Alaska National Wildlife Refuges volunteer Beth Sullivan surveys for the invasive plant elodea at Campfire Lake on the Kenai National Wildlife Refuge on Aug. 30, 2023. Here she pulled up a rake full of star duckweed (Lemna trisulca). (Photo by Matt Bowser/USFWS)

U.S. Fish and Wildlife Service Biological Technician Steve Hoekwater collects an eDNA water sample from Berg Lake on Kenai National Wildlife Refuge on June 7, 2023, as part of an effort to detect invasive northern pike (Esox lucius). Photo by Nathan Davis/USFWS