Fishing should be better on northern portions of the reservoir this year

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By Andrew Johnson ajohnson@aberdeennews.com

Lake Oahe’s fishery is still recovering from the devastating 2011 Missouri River flood, but recent research and surveys by the South Dakota Game, Fish and Parks Department have shown an increase in prey fish numbers and improved walleye condition.

This is good news for anglers, especially those who choose to fish in the northern portions of the reservoir from Akaska to Pollock, said Mark Fincel, GFP senior fisheries biologist in Fort Pierre.

“Things are looking very, very good from Swan Creek north,” he said. “The walleyes up there are looking really good — much plumper, much better. Overall numbers of walleyes are still lower than what we saw in 2009 and 2010 before the flood, but they’re definitely rebounding.”

Conversely, Fincel said the lower end of the Oahe, from Whitlock Bay south to the dam near Pierre, is still struggling to produce the numbers and size of fish that anglers were accustomed to prior to the flood.

“Numbers are still down on the lower end, but that area was the hardest hit and slowest to recover from the flood,” he said. “It’s good news on the northern end, though, because we’re seeing a good recruitment of fish, and the fish we’re seeing are doing well.”

Prey fish resurgence

Fincel said the walleye population’s healthy rebound is due, in part, to record numbers of lake herring, a cool-water prey fish, being marked in Lake Oahe. For the past several years, herring have provided a much-needed forage base for Oahe walleyes after the reservoir’s smelt population was decimated by the 2011 flood.

Oahe Dam was designed with mid-water intakes that draw the deeper, colder water that rainbow smelt call home. So, when the floodgates were opened, a majority of the reservoir’s rainbow smelt population were rinsed through the dam, and walleyes were left searching for a new food source.

Historically, lake herring reproduce and recruit better in times of low smelt populations, but the problem with lake herring is that they often grow too large to eat for predator fish such as walleyes, salmon and northern pike.

However, Fincel said lake herring in Oahe haven’t grown as fast as expected.

“We had very, very strong year-classes of lake herring in 2011 and 2012,” he said. “They are dominating our deep water gill nets, but we’ve noticed there is significant stunting with those year-classes. There’s so many out there that they’re not growing, and right now they’re the perfect food for walleyes and other sport fish.”

In addition, Fincel said gizzard shad, a warm-water prey fish, are also helping Oahu’s gamefish populations make a comeback. He said GFP stocked Lake Oahe with gizzard shad from 2012 to 2014, but GFP has recently found juvenile shad in Oahe — evidence that natural reproduction was taking place. In fact, shad have been found lake wide in 2016 and 2017, and Fincel said he hopes he can say the same thing this spring when the ice finally leaves Oahe.

“We’ve had a pretty hard winter, so we hope the gizzard shad survived,” he said. “They’re a warm-water species, so one thing about them is they die pretty easy from harsh winters.”

Perhaps the best news is that the smelt population has returned to pre-flood numbers, Fincel said.

According to GFP estimates, of the 80 million cold-water prey fish recorded in Lake Oahe last year, roughly 55 million are believed to be rainbow smelt.

Prey fish tendencies

The abundance of prey fish is a Catch 22 of sorts, because fat, healthy fish are ultimately harder to catch. What’s more, Fincel said that having three baitfish options roaming the reservoir will likely force walleye anglers to change their tactics on the fly this spring and summer.

For starters, Fincel said anglers need to understand the tendencies of each prey fish species, as that will likely dictate what types of fishing presentations anglers will need to use to be successful.

“Gizzard shad, for example, are a warm-water fish that are usually found in less than 15 feet of water,” he said. “They’re also a schooling fish, so they’ll bunch up in big, huge schools. Sometimes they’ll move offshore, but then move back into the warm-water bays.”

At the other end of the baitfish spectrum are rainbow smelt, which are a cold-water species. Fincel said smelt would always run deep — below 60 to 70 feet — and be beneath the lake’s thermocline, which is the transition layer between deep, cold water and warmer surface water within the water column.

Last but not least, Fincel said lake herring are more of a cool-water prey fish that like to roam around throughout the water column.

“Lake herring will be found anywhere from 25 feet down through the thermocline to 60 or 70 feet deep,” he said. “Fishing all depends on where the prey is, and that will dictate if the walleyes will be shallow or deeper and might change their behavior. It’ll definitely keep anglers on their toes this year.”

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