Research to map risk of invasive elodea in Alaska

June 15, 2016

John Morton photo. Toby Burke from the Kenai National Wildlife Refuge uses a modified chimney sweep to sample elodea living under a layer of ice in January 2013.

Bodies of water throughout Alaska are at risk for being inhabited by elodea, an invasive water weed that can interfere with salmon spawning and deplete lake nutrients. New research aims to inform resource managers about costs and benefits of managing elodea, and prioritize areas most at risk for invasion.

Tobias Schwörer, a researcher at the University of Alaska Anchorage Institute of Social and Economic Research, is leading a project to identify where elodea is likely to spread and to evaluate future management options. Schwörer is also pursuing a Ph.D. at the University of Alaska Fairbanks School of Management.

Elodea was originally introduced into Alaska as an aquarium plant. The rugged weed can affect water nutrients such as oxygen and can outcompete native plants to grow in dense mats in sandy habitats along lake shores where salmon like to spawn.

The weed can also get tangled in floatplane rudders and boat propellers and impair motor function.

Schwörer first considered the effect of elodea on salmon to assess possible economic consequences for Alaska’s salmon fisheries. Now he is working with floatplane pilots across the state to better map out potential elodea outbreaks and evaluate high-risk locations. The information will be useful to managers and decision-makers to determine how to minimize the spread of elodea and evaluate the best spots to eradicate the species.

“Toby’s research will help us identify locations where pilots are landing more frequently, and that should translate into an enhanced ability to understand where elodea is going to spread next,” said Joe Little, Schwörer’s adviser and an economics professor at UAF.

Schwörer pooled insight from salmon experts with experience studying salmon ecology and management. He presented habitat scenarios that varied in terms of location of elodea, degree of elodea cover, amount of dissolved oxygen, number of predators and amount of prey. The experts were asked to choose which scenarios were most likely to support a persistent population of salmon for the next 20 years.

He found that on average, the experts anticipated that growth rates for salmon in elodea-infested waters would range from minus 5 percent to 1 percent. Growth rates of less than 1 percent represent decreasing population sizes.

Schwörer is also estimating potential economic damages for floatplane pilots who operate in waterbodies likely to be infested by elodea. Pilots around Alaska were interviewed about where they fly, number of flights per season, likelihood of flying to a lake covered with vegetation, income and travel costs.

“Once we have the information from this survey, we can create a map of water bodies that are at risk of elodea outbreaks because of predicted floatplane activity,” Schwörer said.

Climate change is projected to increase the number of invasive species that spread to Alaska. Understanding the most efficient way to determine areas and economies most at risk will become increasingly important.

Schwörer and Little are working with researchers from the UAF School of Fisheries and Ocean Sciences, UAF SOM, U.S. Fish and Wildlife Service, Alaska Department of Natural Resources, and Alaska Department of Fish and Game. The project received funding from Alaska Sea Grant, the Alaska Sustainable Salmon Fund, ADNR, ADFG and the Cook Inlet Aquaculture Association.

ON THE WEB: Read more here.

Heather Stewart photo.. A floatplane sits in an elodea-infested in Sand Lake, Anchorage.