Sub-ice thermal gradients strongly influence winter depth use of an iconic cold-water fish.

Lake Trout (Salvelinus namaycush) winter depth use in thermally stratified lakes is strongly linked to the depth of the 2 °C isotherm.

• Why it matters: Winter inverse stratification (0–4 °C) is less studied than summer, yet it likely shapes where cold-water predators can persist and feed.
• What they did: Using multiyear acoustic telemetry from 11 lakes, the study related winter habitat use to thermal structure, including selection ratios and the depth of the 2 °C isotherm.
• The result: In lakes with depth-averaged temperatures above 2 °C, Lake Trout used thermal habitat averaging 2.6 ± 0.6 °C at 0.1–11.3 m, while in one lake with maximum temperatures below 2 °C they used 16.8–26.4 m with 1.5 ± 0.4 °C; model projections for 877,927 lakes predicted 73% of 66,500 known Lake Trout lakes have warmer winter conditions with upper-column use.

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