Research will map risk of invasive aquatic weeds in Alaska

Anchorage, AlaskaWaterbodies all over Alaska are at risk for being inhabited by elodea, an invasive waterweed that can interfere with salmon spawning and deplete lake nutrients. New research aims to inform resource managers about the costs and benefits of managing elodea, and prioritize areas that are 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 PhD at the University of Alaska Fairbanks School of Management.

Man standing on frozen pond, getting sample of green weeds from the water

Toby Burke from the Kenai National Wildlife Refuge samples elodea living under a layer of ice with a modified chimney sweep in January 2013. Photo by John Morton.

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. This information will be useful to managers and decision-makers looking to determine how to minimize the spread of elodea and evaluate the highest priority 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 associate professor of economics at UAF.

Elodea was originally introduced into Alaska as an aquarium plant. The weed is rugged and can easily spread and outcompete native plants. Elodea grows in dense mats along lakeshores, in sandy habitats where salmon like to spawn. Spawning can be impaired as the density of elodea increases, because elodea can decrease oxygen supply for fish and crowd out fish habitats. On the other hand, elodea can increase productivity in a waterbody and serve as a nursery for juvenile salmon, which may benefit salmon populations.

The weed can also get tangled in floatplane rudders and boat propellers and impair motor function. Case studies from other regions of the United States show that property values may decrease up to 25% near lakes infested with aquatic weeds like elodea.

Native plants, on the other hand, typically die or become dormant in the fall when ice cover begins to form. Elodea, however, can photosynthesize under two feet of ice and can persist after being frozen into ice. The plant reproduces asexually when it is torn apart, which can happen from river travel, ice motion, or removal tactics involving chopping and collecting elodea material.

When elodea spreads quickly, it can use up a lake’s nutrient supply. Because of this ability to decimate the nutrients in an ecosystem, elodea typically has boom and bust growth behavior that can affect oxygen levels critical for fish.

The project has a number of collaborators and has garnered broad support. Schwörer and Little are working with UAF School of Fisheries and Ocean Sciences professor Milo Adkison, UAF School of Management professor Jungho Baek, John Morton and Greg Hayward from the US Fish and Wildlife Service, Heather Stewart from the Alaska Department of Natural Resources, and Tammy Davis from the Alaska Department of Fish and Game. The project received funding from Alaska Sea Grant, Alaska Sustainable Salmon Fund, Alaska Department of Natural Resources, Alaska Department of Fish and Game and the Cook Inlet Aquaculture Association.

“Toby came to me with this project idea, and has done an exceptional job getting the right people to contribute,” Little said.

To consider how elodea could affect salmon, Schwörer pooled together insight from salmon experts with substantial research experience studying salmon ecology and management. He presented a number of 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.

float planes docked around a lake, with green plants in the water

Floatplanes sit in elodea-infested waters in Lake Hood. Photo by Scott Christy.

“This research revealed that most experts believe elodea outbreaks will have a negative impact on growth rate and salmon population sizes,” Schwörer said. He found that on average, the experts anticipated that growth rates for salmon in elodea-infested waters would range from minus five percent to one percent. Growth rates less than one percent represent decreasing population sizes.

For the second part of his study, Schwörer is estimating potential economic damages for floatplane pilots who operate in waterbodies that are likely to be infested by elodea. Pilots around Alaska were interviewed about their flight history, including where they fly, typical number of flights per season, and if they are less likely to fly to a lake that is covered with vegetation. To evaluate how the value of the operation might change for pilots based on elodea outbreaks, Schwörer is also asking the pilots about income and travel costs.

So far, the interviews have revealed that many Alaskans are worried about the negative impacts the spread of elodea could have on their business.

“Once we have the information from this survey, we can create a map of waterbodies that are at risk to elodea outbreaks because of predicted float plane activity,” Schwörer said. This information can be used to create a strategy to minimize the spread of elodea.”

Woman in waders holding up elodea sample

Elodea is dense in the Chena Slough in Fairbanks. Photo from the Fairbanks Soil and Water Conservation District.

By combining an understanding of where elodea will spread and how it is likely to affect salmon fisheries, resource managers will be able to evaluate possible solutions to regional elodea infestation based on the science as well as projected economic costs.

Climate change is projected to increase the number of invasive species that spread to Alaska. The researchers hope this framework for evaluating the risk of elodea could be applied to other invasive species as well. Understanding the most efficient way to determine areas and economies that most at risk for invasive species will become increasingly important.

Little explained Alaska is under financial pressure to maintain critical environmental functions at reduced costs. “Funds and resources are limited, so total eradication of an invasive species may not be an option,” he said. “Under limited budget scenarios, it is important to apply the resources we have to the areas that are the most at risk. That’s one major place where the value of this approach is clear.”


Tobias Schwörer, Senior Research Professional, UAA Institute of Social and Economic Research, 907-786-5404,

Joe Little, Associate Professor of Economics, UAF School of Management, 907-474-2711,

NR: SG-2016/NR309