AUTHORS: Kayla Lenz, Great Lakes Indian Fish and Wildlife Commission; Aaron Shultz, Great Lakes Indian Fish and Wildlife Commission; Adam Ray, Great Lakes Indian Fish and Wildlife Commission; Carl Klimah, Mille Lacs Band of Ojibwe
ABSTRACT: Mille Lacs Lake located in the 1837 Ceded Territory in central Minnesota offers a unique site for assessing the movement of fish throughout a large temperate lake. The relative shallowness of the lake and resultant lack of a thermocline allows ogaawag (walleye Sander vitreus) to forage throughout the lake, thus maximizing their range. Ogaawag , have been impacted by the many changes happening in this system over the past several decades, resulting in a variable but overall decreasing population between 1980 and 2016, when the population seems to have plateaued. This decrease has largely been attributed to a decrease in annual recruitment from hatching to age-2, but the root cause of that recruitment problem is yet unclear. In other large lake systems, ogaawag frequently display spawning site fidelity, making them especially reliant on a relatively small spawning area. Disturbances and changes in these areas may decrease overall reproduction and decrease fry survival. Identifying and protecting these critical sites may maintain annual recruitment of Mille Lacs ogaawag. The purpose of this study was to identify ogaawag spawning sites across years, characterize habitat type, and quantify spawning site fidelity of adult ogaawag in Mille Lacs Lake. Here we examine the movements of 70 tagged adult ogaawag during the spawning periods of 2019, 2020, and 2021 to determine the proportion of ogaawag that display spawning site fidelity and which areas of the lake were “hotspots” for spawning. Using an acoustic telemetry array, we examine the relationships between sex, length, detection depth, average residence time at each receiver, and spawning site fidelity to establish patterns of behavior among ogaawag. We found that ogaawag in Mille Lacs display spawning site fidelity at high rates (96%) and identified areas with rocky and/or hard substrate, lots of wind/wave action, and that are near undeveloped shoreline to be hotspots of ogaawag activity during the spawning season. We also observed what is likely an occurrence of skipped spawning in a female ogaa. Findings from this study should be used to create new stewardship plans to protect in-lake, shoreline, and upland habitats near spawning aggregation sites in Mille Lacs Lake. These approaches may be applicable to other large lake ecosystems.
