The impoundments of the Missouri river from Montana to South Dakota fall under this classification. John Cooper is a walleye pro and Secretary of South Dakota’s Department of Game, Fish, and Parks and lives near the banks of Oahe Reservoir.
“You can set your watch by the spawn on Oahe,” Cooper says. “Consistently, for 20 years, it peaks between April 12 and 18. Spawning starts when water temperatures reach 42°F and peaks between 46°F and 50°F. Most fish spawn on shale points and outcroppings in the back third of creek and river arms.” Some fish also spawn on riprap in the lower end of the reservoir near the dam.
Prior to the spawn and just after ice-out, walleyes are already in the vicinity of spawning flats, but they remain relatively deep (20 to 40 feet). “The back third of creek and river arms have silted in,” Cooper says. “Most prespawn fish are where the bottom is rocky, in the zone just ahead of the ‘flattening’ from siltation.” Vertical jigging with minnows is a prime tactic.
After the spawn, “big females don’t stay to recoup,” Cooper says. “They move in search of forage. Smaller males may hold near rocks and boulders adjacent to spawning flats before migrating.
“Water transforms from almost clear to windblown and dirty during this period,” Cooper says. “Most activity takes place shallow, when surface temperatures are between 50°F and 55°F. Plankton blooms draw the baitfish that draw the walleyes, males and females. All are crowded into the top 12 feet of the water column. Smelt, a prime forage, are at 2- to 15-foot depths.”
Early in this period, Cooper throws a #7 Countdown Rapala tight against the bank, working it like a jig along shale and rubble points between the back third and the middle of creek and river arms. A jig-and-minnow, shad-style crankbait, or bladebait also produces. “Once you find fish, it’s possible to follow them day by day as they migrate toward the main reservoir.”
In years of high water, dispersal is slower, Cooper says. In years of low water, it’s much faster. Postspawn is over when fish reach the main reservoir, mingle with other groups, and begin a presummer feeding binge. During low water, this occurs by the end of May, while high water prolongs postspawn into the second week of June.
