Invasive pike can use Cook Inlet to travel between freshwater systems, research finds

a northern pike
Northern pike are not native to Southcentral Alaska, but biologists have worked for decades to eradicate pike illegally introduced into some Kenai Peninsula lakes. (Kristine Dunker/ADFG)

It was a very ominous discovery back in 2019: invasive northern pike in Vogel Lake, at the tip of the Kenai Peninsula.

And it raised some red flags for biologists with the Alaska Department of Fish and Game. Soldotna-based fisheries biologist Eric Wood said before the Vogel discovery, biologists on the peninsula had only found pike in lakes that were accessible by car. Those pike had likely been illegally put there by anglers.

That didn’t explain why there were pike in Vogel — a remote lake near Point Possession, accessible by float plane or snowmachine.

Now, for the first time, researchers have concrete evidence that the fish could use the ocean to move between freshwater habitats, introducing new questions about where those fish can travel and what scientists can do to keep their numbers under control.

“This discovery kind of opened the door to a whole bunch of other concerns and questions and things we need to figure out,” Wood said.

Northern pike are native to interior and western Alaska, not Southcentral.

But they’re a popular species among anglers. As the story goes, sport fishermen started introducing pike into lakes in the region in the 1950s and then in Kenai Peninsula lakes in the 1970s, likely by way of Fairbanks — causing problems for other fish species. Pike dominate any ecosystem they’re in, eating salmon and degrading local fish populations.

Invasive pike pose a threat to native fish species, like salmon. (Kristine Dunker/ADFG)

Invasive species biologist Kristine Dunker said pike have been found in 150 bodies of water in the region, overall. In the Matanuska-Susitna Borough, researchers have had a hard time getting populations under control.

But on the Kenai Peninsula, the problem has been more manageable. Dunker said over two decades, biologists from a handful of local, state and federal agencies worked hard to eradicate pike on the peninsula.

“And we thought we had. In 2018, we finished a project in the Tote Road area and thought that that was it — that all known populations were gone at that point,” she said. “And it was like, ‘Yay!’ — for about a week.”

That’s when the department heard from an angler who had found the pike in Vogel. The department was also getting word from some setnetters that they were catching pike in Cook Inlet.

With a researcher in Fairbanks, Fish and Game started testing pike to learn whether they had traveled through saltwater. They looked for signs in their otoliths, or ear bones — which can absorb traces of the fish’s environment.

“When we got the results back, you could see on the graph that this fish actually came from somewhere, spent time in saltwater, and then went to a different freshwater location,” Dunker said. “That was very eye-opening to us.”

Vogel Lake
Biologists first found a pike in Vogel Lake, shown above, in 2019. (Kristine Dunker/ADFG)

Wood said that ocean pathway could complicate efforts to contain pike, and he said inlet conditions could become more favorable for the freshwater fish as glaciers continue to melt.

“As to where they came from, how they ended up where they ended up, we don’t know that for sure,” Wood said. He added that the Susitna River seems to be the obvious point of origin, since pike are so widespread there.

Wood and Dunker both said from the research side of things, the new discoveries are fascinating. Now, they’re finding marine signatures in pike from other systems too, including two lakes in Anchorage earlier this year — Campbell Lake and Westchester Lagoon.

But the findings create more challenges on the management side.

Dunker said since pike disperse, it’s important to prevent populations from spreading.

“The big challenge for us now is to try to figure out — How do we do that well? When you have a scenario where pike could be moving around marine estuary corridors, that makes it a much more difficult problem. But it doesn’t make it an impossible one,” she said. “It just means we have to be kind of smart about it and anticipate where they might be going.”

Wood said Fish and Game has already put a weir at Miller Creek, which flows out of Vogel Lake, to stop northern pike from entering the system there. But he said that’s not a permanent solution.

“The reality of it is, there’s so much money, so much tradition and everything tied up with salmon in this area, that this could have the potential to wipe out so much,” Wood said. “So it is scary, in that way.”

With many questions remaining, Dunker said every fish they can test and study is helpful. She said anglers and fishermen who catch pike should report their sightings to Fish and Game and bring in retained pike, when possible. The number to report invasive pike is 1-877-INVASIV.

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