Invasive plant could cost salmon industry $159 million per year, ISER study finds

Published: Oct. 14, 2019 at 12:12 PM AKDT
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A common aquarium plant illegally dumped into Alaskan waters that has adapted to cold weather could threaten wild salmon habitat and cost the commercial fishing industry hundreds of millions of dollars.

A recent study conducted by ISER, the Institute of Social and Economic Research, found that if not managed, the cost of the elodea invasion could cost the commercial sockeye fishing industry $159 million

each year

. They even say that there is a 5% chance that the costs could exceed $577 million annually.

Elodea is Alaska's first invasive aquatic plant and has spread across the state in the past decade.

"Ultimately what elodea does is it out-competes other aquatic plants and what it does is it'll get so thick that it can hinder boats getting through it, float planes getting through. And obviously if it's that thick the kinds of conditions set up, you can have what we call anoxic conditions where there's just not enough oxygen in the water to support fish," said John Morton, Supervisory Biologist at the Kenai National Wildlife Refuge. "And certainly for things like lake-spawning sockeye salmon, you need gravel beds to put their fish redds in there."

Although the state's first documentation of elodea was in Cordova in 1982, there was no aggressively-growing population of the plant found until it was discovered in Chena Slough near Fairbanks in 2010. The discovery in Fairbanks prompted research economist Toby Schwoerer to look into the potential economic impacts of the invasive plant.

Along with Schwoerer at the Institute of Social and Economic Research at UAA, an economics professor and a fisheries professor at the University of Alaska Fairbanks used a multi-method approach to gauge the range of potential impacts of the invasive plant.

Since elodea infestations are new to Alaska, there is very little research on its impacts on salmon. The researchers asked more than 50 salmon experts from state and federal agencies as well as university researchers what impacts they believe elodea would have on sockeye salmon.

"Experts believe that the effects on salmon are really quite mixed. There could be potentially some positive, but primarily we found negative effects," Schowerer said.

Lowered levels of dissolved oxygen, loss of suitable spawning habitat and improved habitat for northern pike were some of the factors that could harm salmon productivity. Potential benefits included increased prey for young salmon.

"These are all different factors that we tried to account for in our expert elicitation, then ask 'what do you think? Would salmon persist in elodea invaded salmon habitat or not and to what degree? What would the growth rates be you would expect?'" Schwoerer explained. "So from that, included in a market analysis, we could then estimate the costs for the society, or say for consumers, of the damages to wild Alaska sockeye salmon."

The researchers estimate that if elodea were to remain unmanaged, the most likely average damages to the commercial sockeye fisheries across Alaska would be $159 million annually, with a 5% change of exceeding $577 million annually.

"At this point I think invasive species have kind of been overlooked as just a problem that many believe is just starting in the state," Schwoerer said. "So it's really, I believe, a wake up call for our state to think about whether we want to do something about aquatic invasive species, and it also showed the value of prevention."

An adapting infestation

Morton says that the belief among biologists is that the initial infestations across the state in Cordova, the Kenai Peninsula, Anchorage and Fairbanks resulted from people dumping their aquariums into a body of water.

Biologists have since seen elodea in Alaska that has adapted to be acclimated to the cold, posing both a greater risk for more rapid spread but also a unique opportunity for treatment.

"During the initial period - and this is very common when invasives first get introduced - is we think what happened is it stewed, literally, for around 15 years. Elodea comes from the Midwest, so it's quite a bit warmer there and it basically had to become cold-adapted," Morton said. "The difference now is we have cold-adapted populations that are being moved around the state by float plane."

Photo from Kate Mohatt/U.S. Forestry Service

Morton says biologists with U.S. Fish and Wildlife Service have documented elodea continuing photosynthesis under snow covered ice in winter when native plants are dormant. The result is an invasive plant that if not treated can quickly overtake native plants. Morton says he has seen explosive growth in Sports Lake near Soldotna and at Alexander Lake in the Mat-Su Valley.

"We've seen it go from a few plants to occupying the entire lake within a year. It's really incredible. It's just like, 'boom!'" Morton said.

A potential solution

Since the most native aquatic plants are dormant during the winter, managers are able to chemically treat elodea with minimal damage to other plants.

The primary chemical to eradicate elodea is fluridone. The chemical is a systemic killer. Morton says when used at five to 5 to 10 parts per billion over periods longer than a year, it kills elodea with little impact on native aquatic plants. Another chemical used to treat elodea is diquat, a chemical that kills aquatic plants on contact. Diquat is cheaper than fluridone, but it kills all aquatic plants it touches.

Until recent weeks, there had been five known instances of elodea on the Kenai Peninsula and each has been successfully eradicated. In September, a biologist with Alaska Department of Fish & Game found elodea in a Sandpiper Lake while looking for northern pike. Morton expects treating the new infestation would cost around $40,000.

This summer ADF&G closed Alexander and Sucker Lakes in the Mat-Su Valley were closed to sport fishing while the lakes were being treated for elodea. The Department of Natural Resources estimated the first year of treatment for the lakes would cost around $850,000.

The DNR quarantined elodea statewide in 2014, meaning that the plant cannot be shipped, sold or transported in Alaska, yet Schwoerer feels that his study suggests the state and federal agencies should consider more proactive preventative steps.

"This study really showed the value of preventing aquatic invaders from coming to Alaska's pristine salmon watersheds, and I think it makes a good case for putting investments towards preventing further aquatic invasive species from coming to the state," Schwoerer said.

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