Data and code from: Brook trout thermal habitat selection in stratified lakes: diel patterns, body size, and the importance of thermal time

Thermal habitat selection is a key consideration when assessing the
capacity of ectotherms to tolerate warming conditions during summer. We
used high dimension acoustic arrays in three lakes to determine diel
thermal habitat selection by free-ranging adult brook trout with
surgically implanted acoustic tags (fork length range, 26.2–54.5 cm).
Brook trout occupied a range of temperatures during lake stratification
when warm surface waters and cold hypolimnetic waters were present. The
overall mean occupied temperature was close to literature estimates of a
single preferred temperature (15°C), but few individuals spent most of
their time at this temperature. The preferred temperature range was
13–17°C in each lake while < 10°C and > 20°C were avoided.
Individual variation was extensive and closely associated with body size.
Despite wide diel variation in patterns of thermal habitat selection,
thermal time (degree-hours; °C-hrs) was consistent and inversely related
to body size over a month. Large adult brook trout accumulated fewer
degree-hours than smaller brook trout. The intercept of this relationship
was close to their sublethal threshold as defined by physiological stress.
We hypothesize that adult brook trout actively manage metabolic rate as a
function of body size over periods greater than the diel cycle.