State, refuge to tackle invasive pike problem

The species threatens native fish populations in the area, including rainbow trout and juvenile salmon.

Pike prey on rearing salmon. (Alaska Department of Fish and Game)

Pike prey on rearing salmon. (Alaska Department of Fish and Game)

The Kenai National Wildlife Refuge and the Alaska Department of Fish and Game will collaborate to eliminate the peninsula’s remaining pockets of invasive pike populations, in the Miller Creek Watershed west of Hope. Self-sustaining pike populations were detected in Vogel Lake, North Vogel Lake and the upper portion of Miller Creek, which flows from the lake into Cook Inlet.

The species, the groups say, threatens native fish populations in the area, including rainbow trout and juvenile salmon.

Pike are native to parts of Alaska north of the Alaska range, but were illegally introduced in Southcentral Alaska to Bulchitna Lake in the 1950s. That population expanded quickly following natural dispersion and additional illegal introductions.

The first pike on the Kenai Peninsula are thought to have been introduced at Derks Lake in Soldotna, where they were able to spread to other waters via drainage and additional illegal introductions. By the 2000s, Massengill said, dozens of bodies of water on the Kenai Peninsula were infested with pike.

To date, Massengill said sustainable and reproducing populations of pike have been detected in roughly two dozen water bodies on the Kenai Peninsula. The populations in Vogel Lake, North Vogel Lake and the upper portion of Miller Creek are the last known pike populations on the peninsula.

Massengill said there is some evidence to suggest that the illegal introduction of pike in Southcentral Alaska was the result of a desire to start a new fishery.

The problem with pike is that they’re highly piscivorous, or fish-eating, according to the Alaska Department of Fish and Game. They are officially considered an invasive species in Southcentral Alaska because they are non-native and can cause harm to the environment, to the economy or to human health.

“[In] nearly all water bodies where pike have been long established on the Kenai Peninsula, native fish populations have declined or have been completely eliminated,” Massengill said.

In addressing the problem of invasive pike in the Miller Creek Watershed specifically, the draft environmental assessment identifies four potential plans of action.

The first alternative is to do nothing. Doing nothing to address invasive pike in the watershed would allow the population to grow at a rapid pace and could result in the elimination of the rainbow trout population in those waters.

The second option is to net and contain the pike. This would involve “excessive” gillnetting of pike in Vogel Lake, however, the alternative acknowledges that suppressive gill netting would likely have to be perpetual “and may ever completely remove pike from the project area.” Additionally, this option would place barriers at certain locations of Vogel Lake to ensure that pike cannot enter neighboring water systems. Those barriers would only be in place when netting occurs.

Alternative three would use the pesticide Rotenone, which has historically been used for fish management. Rotenone is effective at killing fish because it impacts the oxygen transfer needed for cellular respiration.

Alternative four is a combination of alternatives two and three. In addition to an aggressive gill netting strategy and the implementation of temporary barriers, alternative four would also see the use of Rotenone to manage the fish.

First, as many native fish as possible would be removed from the waters for safeguarding purposes. Next, temporary would be maintained to keep pike from invading nearby systems. After that, rotenone would be applied to the waters with the goal of killing the pike. Then, gill nets would be placed in the area to evaluate the effectiveness of the rotenone and to remove any pike that may not have died. Once pike were confirmed to have been eliminated, the barriers would be removed and water quality would continue to be monitored.

Massengill said Friday that rotenone has historically proven to be the most effective way of eliminating pike populations on the peninsula. ADFG has sometimes been successful at removing pike by gillnetting alone, but in those cases the size of the water body was small — less than 40 acres — and the fish population was small.

Massengill said rotenone has been used to manage fish populations in the United States in the 1930s and is particularly effective because it stops cell respiration when absorbed through gill membranes. Rotenone is best used when initially administered in the fall because it lasts longer when it is cold and cloudy outside.

The U.S. Environmental Protection Agency, Massengill said, is in the process of re-registering rotenone products and recently said that when rotenone is applied to water at 90 parts per billion or less, there is no concern about people coming into contact with water, such as for purposes like swimming. When applied to water at 40 parts per billion, which is the rate typically used to get rid of pike, there aren’t concerns about people drinking the water.

“The EPA says that you can drink the water — there’s no drinking concern for humans at that level,” Massengill said. “We don’t advise drinking it, but that’s how the EPA looks at the safety of right now.”

The biggest threat rotenone poses is to the people administering it who may inhale particles if the rotenone is in powder form. The pesticide is not carcinogenic and does not cause cancer, but can cause symptoms similar to those experienced by people with Parkinson’s disease.

The pesticide will not do anything to Cook Inlet fisheries, Massangill said. The levels of rotenone in water flowing into Cook Inlet will be so low that the EPA considers it to be deactivated. To treat the Miller Creek Watershed, Massengill said it would take about four to five days and would likely rely on aerial and boat transportation.

Miller said Friday that once the public comment period is over, they will be able to incorporate the feedback they received into narrowing which alternative they want to pursue. Regardless of which alternative they select, Miller said they hope to begin work on the project as early as this fall and to at the very least have chosen an alternative by the end of May.

Public comments on the draft Environmental Assessment can be submitted until April 17 by mail or by email at benyamin_wishnek@fws.gov. Written comments can be addressed to Ben Wishnek, Kenai NWR, P.O. Box 2139, Soldotna, AK 99669.

Reach reporter Ashlyn O’Hara at ashlyn.ohara@peninsulaclarion.com.

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