What is it about?
Where do lake trout go in winter? While these cold-water fish typically stay in deep water during summer, their winter habitat can be surprisingly different. Some swim close to the surface beneath the ice, while others remain much deeper. In this study, we combined 32 years of water temperature measurements and fish-tracking data from 11 North American lakes to understand how lake trout choose their winter habitat. We found that lake trout tend to prefer water temperatures around 2°C, but the depth of this preferred temperature varies greatly among lakes. In smaller, deeper, and more sheltered lakes, lake trout generally occupy shallower waters. In contrast, in larger, wind-exposed lakes, they tend to stay much deeper. These differences are largely explained by how lake shape and wind influence water temperatures before ice forms.
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Why is it important?
Most studies of lake trout have focused on summer, leaving their winter habitat use poorly understood. Our study shows that water temperature plays a key role in determining where lake trout live beneath the ice. We found that lake trout preferentially select depths near the 2°C temperature boundary, which varies with lake shape and wind exposure. By combining fish-tracking data with water temperature measurements from 11 lakes over 32 years, we provide a new way to predict winter fish habitat across lakes. These findings can help us better understand how changing ice conditions and climate warming may affect cold-water fish and support future fisheries management and conservation.
Perspectives
The inspiration for this study came from an earlier paper from Prof. Mathew Wells (Yang et al. 2021), which explored how lakes develop different thermal structures beneath winter ice. Building on this work, I became interested in whether these differences could explain why lake trout occupy different depths across lakes. By combining lake physics with fish telemetry data, we were able to explore this question across a wide range of lakes. I am particularly grateful to Professor Mathew Wells for his supervision, encouragement, and many insightful discussions throughout this project. I also sincerely thank all our collaborators for sharing their valuable datasets, expertise, and ideas. This study would not have been possible without their support and contributions.
Lidi Shi
University of Toronto
Read the Original
This page is a summary of: Sub-ice thermal gradients strongly influence winter depth use of an iconic cold-water fish, Proceedings of the National Academy of Sciences, November 2026, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2600502123.
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