Data from: Thermal habitat fragmentation in stratified lakes induces resource waves that brook charr track across seasons

The spatial configuration of thermal habitats constrains the
thermoregulatory performance of ectotherms. Thermal landscapes also vary
through time, which is particularly relevant in seasonal environments such
as temperate lakes. Indeed, elevated temperatures in the epilimnion of
dimictic lakes during summer could substantially reduce the use of this
habitat by cold-stenothermic fish during the stratified period. The main
objective of this study was to evaluate whether thermal habitat
fragmentation in stratified lakes modulates accessibility to resources
that brook charr, Salvelinus fontinalis, which is a mobile consumer, can
track across seasons. More specifically, we hypothesize that reduced
access to the littoral habitat during summer enhances foraging
opportunities in this habitat during winter. We used an automatic acoustic
telemetry system offering full coverage of the lake to continuously record
brook charr locations across seasons, and we estimated zoobenthos
abundances in the littoral habitat using image processing and
semi-automatic classification. While brook charr concentrate in the
metalimnion of the pelagic habitat in summer, most individuals in winter
shift to a shallow bay that is unexploited in summer due to thermal
constraints. In this habitat, zoobenthos abundance is more than twice as
high at the end of the summer compared to littoral habitats close to the
thermal refuge in the pelagic habitat. Surprisingly, brook charr showed
strong within-lake site fidelity between two consecutive summers, which
suggests that spatial memory could be a key driver of seasonal habitat use
in this lacustrine population. Overall, our results suggest that thermal
barriers create fragmentation between littoral and pelagic habitats that
in turn produces resource opportunities that brook charr can track across
seasons.