Figure 4.

Maximum heart rate (f_Hmax) of anadromous Arctic char during acute warming from 5°C (orange; n = 12) and cooling from 10°C (blue; n = 8) as (a) individual and (b) average responses. The cumulative proportion of individuals that reached their temperature at peak f_Hmax (T_peak) and arrhythmia (T_arr) are inset (b). The thermal sensitivity of f_Hmax is shown using (c) the temperature coefficient (Q₁₀) calculated over 2°C increments, with reference lines indicating rates of change that would correspond to a doubling (2.0), plateau (1.0) or halving (0.5) of f_Hmax over 10°C and (d) an Arrhenius plot of f_Hmax showing the first Arrhenius break points during warming (T_warmAB) and cooling (T_coldAB). Averaged data (b–d) are presented ± sem and dashed connecting lines with open circles indicate temperatures where some individuals were removed from the analysis following arrhythmia.