Inter-annual changes in winter conditions elicit changes in fish behavior under lake ice

Winters are warming faster than other seasons, and ice cover duration on temperate lakes is shortening. How ectotherms respond to these changes during poorly studied winter periods remains unclear. Here, we use acoustic telemetry to determine whether the same individuals of a model warm-adapted fish, smallmouth bass (Micropterus dolomieu), change their depth and space use to maintain consistent experienced temperatures and low activity across three winters with different conditions. Despite considerable variability among individuals, the population demonstrated plasticity in depth use that regulated experienced temperatures across warmer (year 1) to colder (year 2) to shorter (year 3) winters. Activity was low during all winters but increased 2 weeks earlier when temperatures warmed earlier in year 3, consistent with previous reports of earlier overwinter emergence in terrestrial ectotherms under a warming global climate. Whether consumption rates increased with increasing temperatures determined the bioenergetic outcomes of earlier spring warming. This study demonstrates that ectotherms that spend winter in a state of reduced activity can behaviorally respond, at individual and population levels, to changing winter conditions. Variation in winter habitat use and activity could have consequences for reproduction and growth in open water seasons and remains an important area for future research.