The South Dakota Game, Fish and Parks Department’s summer Missouri River fish surveys have been completed and early observations show both good news and a bit of bad news for Lake Oahe’s most popular game fish.
It’s a little early to know for sure what the surveys will show for Lake Oahe, said Fisheries Biologist Mark Fincel, but there are some positive signs. A lot of gizzard shad were caught in the department’s warm-water bait fish seine-net survey. Meanwhile, deep water gill nets in the lake caught plenty of lake herring, which serve as a high-calorie food source for large walleye and salmon.
“We have lake herring coming out of our ears still,” Fincel said.
With plenty of food in the lake, walleyes seem to have fared pretty well, Fincel said. The fish caught in the annual gill-net population surveys were in good condition, he said. That makes things tough on anglers.
“It’s that double edged sword,” Fincel said. “When there’s more bait fish in the lake … everything does better, well, except for the anglers.”
As a general rule, well fed fish are harder to catch.
Another problem was that walleye numbers in the lower portion of the lake have fallen from recent highs.
“Lake Oahe is still in recovery,” Fincel said by way of explanation.
Walleye abundance in Lake Oahe from Whitlock Bay to Oahe Dam was down in 2016 and this year’s surveys may not show much improvement, Fincel said. That’s a product of two things. The first would be the lake’s struggle to rebuild its coldwater baitfish population, which mostly consisted of rainbow smelt. The smelt population was devastated during the 2011 flood by being sucked through dam.
Rainbow smelt are a fatty fish and don’t grow much more than nine inches long, which makes them an ideal food source for 20-inch and bigger walleyes. Smelt numbers have remained pretty low since 2011.
Meanwhile, 2009 saw one of the best walleye spawns in Lake Oahe’s history. After the 2011 flood flushed Lake Oahe’s cold water bait fish through the dam, the walleye born in 2009 started growing more slowly. Instead of taking three years to reach the most desired 15-inch and bigger size range, they took four or five years.
Through much of their prime spawning years, those 2009 fish were struggling, which appears to have led to a decrease in spawning success. In 2011, another big walleye spawn added more fish to the mix and they too were slow to reach the 15-inch size range.
Lake Oahe’s walleye tend to start dying off by the time they turn six, so by now those 2009 fish have all but disappeared from the lake. The fish from 2011 also will have begun to rapidly die off.
The GF&P took steps this year to try and jumpstart lower Lake Oahe’s walleye population. About 300,000 fingerling walleyes were stocked between five locations, Chantier Creek, Okobojo Point, Cow Creek, Spring Creek and Peoria Flats. By a stroke of luck, another 4 million walleye fry were dumped into the lake near Minneconjou Creek.
“There were extra fish at the hatchery,” Fincel said.
Cold water baitfish seem to be making a bit of a recovery. For the last three years or so, fat-filled lake herring have helped narrow the dietary gap for bigger game fish. Salmon, in particular, seem to have benefitted from increased numbers of lake herring.
Combined with high numbers of warmwater prey such as gizzard shad, the walleye have been getting healthier, which could lead to better spawns and eventually more 15 to 20-inch walleye, Fincel said.