THE ROLE OF AQUATIC MACROPHYTES IN PROVIDING THERMAL REFUGIA FOR WALLEYE

Anthropogenic stressors such as habitat loss, species introductions, and overfishing have influenced fisheries for decades and climate change threatens to compound these factors. Within the Midwest United States, Walleye (Sander vitreus) are an ecologically, economically, and culturally important coolwater fish that are threatened by loss of critical coolwater habitat. Aquatic macrophytes have been proposed as thermal refugia in littoral areas of lakes due to shading and limiting mixing of surface waters by wind, but effects have not been quantified in a whole lake comparative approach. To evaluate macrophytes as potential thermal refugia for coolwater fishes we measured water temperature at 12 littoral sites (1 and 3m) using remote sensors in Sparkling Lake, WI from May-September in 2023. We modeled water temperature at different sites over the course of the summer and quantified macrophyte influence on water temperature. Water temperatures at macrophyte sites were on average 1.13°C cooler over the summer compared to sites without macrophytes. This cooling effect of macrophytes was more pronounced during peak summer and at deeper depths, with maximum differences of up to 3°C. As climate change and warming waters continue to threaten coolwater fishes such as walleye, there is a critical need to quantify habitat that may serve as thermal refugia. Our results suggest that macrophytes may contribute to fine-scale temperature differences in littoral areas and may play a key role in providing these fishes with critical thermal refugia in north-temperate lakes.

Primary Presenter: Quinnlan Smith, University of Wisconsin - Madison (qcsmith2@wisc.edu)

Authors:

Quinnlan Smith, University of Wisconsin Madison - Center for Limnology  (qcsmith2@wisc.edu)

Olaf Jensen, University of Wisconsin Madison - Center for Limnology  (ojensen@wisc.edu)

Jake Vander Zanden, University of Wisconsin Madison - Center for Limnology  (mjvanderzand@wisc.edu)