A comparison of the effects of water-level policies on the availability of walleye spawning habitat in a boreal reservoir

Papenfuss JT, Cross T, Venturelli PA. 2018. A comparison of the effects of water-level policies on the availability of walleye spawning habitat in a boreal reservoir. Lake Reserv Manage. 34:321–333. Water levels in reservoirs can affect the quantity and quality of the habitat that is available for spawning fish and their eggs. We studied how a change in the water-level management policy (“rule curve”) in 2000 affected the availability of walleye (<i>Sander vitreus</i>) spawning habitat in 3 lakes (Kabetogama, Namakan, and Sand Point) that make up a large, boreal reservoir between Canada and the United States. According to observed water-level data, available spawning habitat on known Lake Kabetogama spawning sites increased 95% (<i>P</i> &lt; 0.01) with the 2000 rule curve, but did not change on Namakan or Sand Point lake spawning sites. However, when using modeled water-level data to control for confounding weather events, habitat availability at known spawning sites increased significantly (<i>P</i> &lt; 0.01) on all 3 lakes (179%, 92%, and 93%, respectively). Habitat availability improved because the 2000 rule curve increased mean spring water levels by 0.5 m, and water levels rose more slowly (2.2 vs. 3.0 cm/d) during egg incubation. Our findings suggest that, although water-level management on large reservoirs can be a challenge, carefully designed policies can improve walleye spawning habitat conditions and help to achieve fisheries management goals.