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YANKTON, S.D. (AP) — Wildlife officials in South Dakota and Nebraska are studying why the walleye population is declining at the Lewis and Clark Lake.

The fish’s downturn has been ongoing for nearly decade, the Yankton Press & Dakotan reported .

“Since 2009, population numbers have been going down,” said Chris Longhenry of the South Dakota Game, Fish and Parks Department. “There are a number of possible reasons. Right now, we are working on our stocking evaluation.”

The Nebraska Game and Parks Department stocked a million juvenile walleye in 2014 and 2015. Neither of those stockings managed to stick with the exception of 0.5 percent in 2014 and 10 percent in 2015, according to Longhenry.

Longhenry said there’s no definitive proof of an explanation for the drop but he cited several possible reasons.

“The population could be negatively related to the amount of water that flows through the dam, the population could’ve been too small to avoid it,” he said. “Adult fish possibly moving upstream to the delta or above, or higher flows may be limiting the food base.”

Experts are also concerned that zebra mussels could be negatively affecting the food supply for walleye populations.

“We’re putting out plate samplers up the lake to fort Randall,” Longhenry said. “Thing is going to allow us to monitor zebra mussel colonization, movement and what effect they’re having.”

Researchers plan to continue looking at walleye and zebra mussel for the foreseeable future, as well as other projects set to begin this summer.


Information from: Yankton Press and Dakotan,