The Namakan Reservoir, located on the Minnesota-Ontario border, has been successively managed under two water-level management policies (‘rule curves’) in recent decades. To compare the effects of the rule curves on walleye spawning, I modeled wave energy, ice scour, and habitat availability at 44 spawning locations. Wave energy increased (18% for observed water levels, 6% for modeled water levels) and ice scour decreased 11% (both P < 0.01) over spawning habitat during the most recent rule curve. Observed water level data suggested available spawning habitat on Lake Kabetogama increased 95% (P < 0.01), but availability on Namakan and Sand Point Lakes was unaffected. However, when controlling for weather events, habitat availability increased significantly (Kabetogama = 179%, Namakan = 72%, Sand Point = 93%, P < 0.01) on all three lakes. These findings suggest that the most recent rule curve is likely to improve reproductive success for walleye in the reservoir.
Papenfuss JT, TK Cross, PA Venturelli (2017) Comparing water-level policies in a boreal reservoir: how wave and ice energy can help maintain walleye spawning habitat. Lake and Reservoir Management 33:249-259