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Arctic Grayling Habitat Limited by Chena Slough Invasive

National Park Service

Fairbanks, AK - The Fairbanks Soil and Water Conservation District hosted a public meeting in North Pole Tuesday night to talk about the changing ecology of Chena Slough.  The slough is undergoing along term restoration project after biologists discovered the presence of an invasive aquatic plant and a serious decline in the Arctic grayling population.

In the mid-1990’s the Army Corps of Engineers mapped Chena Slough to assess Arctic Grayling habitat.  Amy Larsen is an aquatic ecologist with the National Park Service.  She repeated that same study in 2011.
“Since this project was done in 1997, there’s been about a 29 to 30 percent reduction in spawning and rearing habitat for arctic grayling," she says.  "This is largely a result of vegetation encroaching into what once was riffles and pools habitat in the stream that had been previously unvegetated.”

Larsen works with Nick Lisuzzo.  He’s a biological science technician with the US Forest Service.  Lisuzzo says Chena Slough is historically one of the most productive streams for Arctic Grayling in North America.
“Prior to the 1960’s, when Fairbanks was flooded and the subsequent development of the Chena Floodplain project,  Chena slough was a side shoot of the Tanana River and had pretty fast slow and had pretty good substrate for Arctic Grayling spawning habitat,” says Lisuzzo.

The floodplain project cut the slough off completely from the Tanana River, so today, it’s fed only by ground water.  Not only did there used to be lots more water in the slough, it was also a lot more turbid.  That means there were all kinds of tiny particles floating around in the water.  Deep pools riffles and gravel along the bottom made excellent habitat for grayling.  Nick Lisuzzo says the Chena flood project isn’t the only reason grayling habitat has diminished. “One of the things we think is likely contributing to that is this nonnative aquatic weed, Elodea,” he says.

Elodea was likely introduced to the slough within the last 10 to 15 years.  It’s taken over almost half of the lower 10 miles of the slough.  The plant can choke out other species.  Amy Larsen says it essentially creates its own habitat. “So, basically the plant comes in, grows, slows down the water, makes it more suitable to for it to grow," she says. "It helps get sediment out of the water, it makes the soil better for the plant to grow.  It’s a positive feedback system and so it’s just gonna continue to fill in the channel over time.”

The Fairbanks Soil and Water Conservation district plans to use a suction dredge to start removing Elodea from the slough next summer.  While the grayling population has decreased in recent years, both Lisuzzo and Larsen say they haven’t completely disappeared from Chena Slough. “I don’t think it’s a serious threat to the grayling pop in the Chena river system itself," says Nick Lisuzzo. "I think it’s more of an issue of local recreational opportunities for residents of North Pole and the Fairbanks area."

“Well, one of the things that has happened," explains Amy Larsen, "is this used to be everybody’s best place to go fishing, from around town and in Fairbanks.  It was a great fishing spot and people could readily go catch really nice size grayling pretty frequently and so that’s really changed over the years," she says. They’re having to spend a lot more time to catch any given fish and also just the navigability of the stream has changed a lot.  You just can’t even paddle because there’s so much vegetation in the slough.”

Nick Lisuzzo says the long term restoration of Chena slough would be nearly impossible without the information collected by the Army Corps of engineers. “In 1997, when the Corps and Fish and Game were addressing this problem," he says, "they actually made these really detailed habitat maps of the entire slough and archived their data and their methodology in pretty good detail and it’s pretty rare that you have the before introduction data.  We’re lucky enough to have that sort of information just lying on the bookshelf somewhere.”

Lisuzzo and Amy Larsen have submitted a manuscript of their work to the North American Journal of Fisheries Management for publication.