Invasive plant poses threat to Alaska sockeye salmon

An invasive, quick-spreading aquarium plant could forewarn of the upcoming difficulties that Alaska salmon runs may face as marine environments change from human intervention.

The plant is elodea, which is native to the lower 48 U.S. states and is commonly used in aquariums. Researchers say it was first dumped into Alaska waters in the early 1980's with the unwanted contents of an aquarium and has since adapted to colder water. Now, it is being transported from lake to lake by float planes and growing at an alarming rate of speed.

Research economist Toby Schwoerer got interested in elodea when two researchers from the University of Alaska Fairbanks stumbled on the plant while sport-fishing in the Chena Slough in 2010.

“They ran into these really thick mats of aquatic vegetation. They were shocked. It took a while to realize what it was, but geneticists basically traced it back to this aquarium plant that is widely used around the country,” Schwoerer told SeafoodSource.

A few years later, Alaska Department of Fish and Game (ADF&G) biologists found the plant in several lakes on the Kenai Peninsula, and then it was found in Lake Hood, Alaska’s largest floatplane base. Planes taking off from Lake Hood are now spreading elodea to remote locations.

The alarming dissemination of the plant prompted Schwoerer and others to study the effect elodea might have on salmon runs, focusing on sockeye, Alaska’s most lucrative species. After talking to around 50 salmon specialists to get their opinions of how the dynamics between elodea and sockeye might play out, the report highlights the uncertainty faced by our ecosystems. According to Schwoerer, most experts pointed to concerns with elodea like lower dissolved oxygen levels, crowding out of salmon redds, and better habitat for sockeye predators like pike.

“Based on how consistent they were, I could then weigh their answers and come up with an aggregated opinion on the range and expected growth rate for sockeye salmon in elodea-invaded habitat. Then I used that information to drive a population dynamics model and then a consumer surplus model,” Schwoerer said.

The model allowed Schwoerer to value potential elodea-related losses to state’s major sockeye fisheries, and he estimated that it could cost the commercial sockeye industry USD 159 million (EUR 144 million) annually, with a 5 percent chance of the cost reaching USD 577 million (EUR 523 million) a year.

Schwoerer also pointed out that the study turned up a 5 percent chance of USD 144 million net positive from elodea, highlighting the uncertainty salmon runs face as ecosystems morph.

But Schwoerer is not suggesting Alaska take a chance on the net positive. The consensus amongst researchers is that the plant should be attacked quickly and aggressively.

“We have a proven, successful management strategy to eradicate it. We’ve eradicated elodea from the lakes on the Kenai Peninsula in just a few years by deploying fluridone,” Schwoerer said.

He added that fluridone, a herbicide, is an effective “scalpel approach,” meaning it is lethal to elodea, but has minimal effect on the native plants and other marine life.

Photo courtesy of Justin Beyerlin/Shutterstock