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Fisheries Biologists Complete Fall Reproduction Survey

Monday, October 15, 2012

The North Dakota Game and Fish Department’s annual fall survey shows low numbers of young-of-the-year fish in the Missouri River System, while Devils Lake once again showed exceptional numbers of young-of-the-year walleye.

Scott Gangl, fisheries management section leader, said the catch at Lake Sakakawea was poor for most species including walleye, especially considering 4 million were stocked this year. “We actually captured some 1-year-old fish that were only slightly bigger than this year’s young-of-the-year,” Gangl said. “The reservoir wasn’t very productive this year given its rapid rate of elevation loss.”

However, Gangl said production of forage fish in Lake Sakakawea has been fairly good over the last few years. “Our size structure and growth rate of our older game fish improved from a decade ago when there was a prolonged period of drought years,” he said.

The Missouri River from Garrison Dam to Lake Oahe showed few young game fish or forage fish. “Fish populations in this stretch of the river are all based on natural reproduction, which was good in 2009-10,” Gangl said. “We have an abundance of adult walleye and pike, but they are on the smaller side because they are only 2-3 years old. In addition, we lost a lot of forage in 2011, and poor reproduction again in 2012 continues to depress the forage base, leaving our game fish on the skinny side and growing slower than we would like.”

This past spring Game and Fish personnel, along with South Dakota Game, Fish and Parks, stocked adult gizzard shad at eight sites throughout Lake Oahe. Gangl said the intent was for adult shad to reproduce and provide young-of-the-year for forage and a seed stock to rebuild the population. “We did detect some reproduction, but it will not be an overnight success,” he added. “We need a few more mild winters like last year before we see a rebuilding of the shad forage base like we had in the early 2000s.”

The rapid loss of water that was witnessed this year in lakes Sakakawea and Oahe is alarming, Gangl said, but decreased system flows this fall will provide some recovery assistance.

Devils Lake showed the second highest young-of-the-year walleye catch rate on record, second only to 2009. “Devils Lake continues to be a walleye factory,” Gangl said. “The high water levels on Devils Lake have improved natural reproduction for most fish species, and there is an abundance of young fish in the system.”

A total of 367,000 walleye were stocked in East Bay and East Devils Lake where natural reproduction tends to be less. However, Gangl said abundant young walleye were seen throughout the lake.

Fall reproduction sampling provides biologists with an index that measures natural reproduction and stocking success. Survey nets are designed for small, young fish which allows biologists to assess reproduction and status of both game and forage fish species. All large and mid-sized reservoirs are sampled every year, and many small lakes are targeted as well.