The effect of diel thermal cycles on growth and performance of wild Atlantic salmon (Salmo salar)

Abstract

As Atlantic salmon populations throughout Atlantic Canada continue to decline, it is important to evaluate the role temperature plays on their survival. Part of this decrease in abundance can be attributed to climate change as streams experience an increase in average summer temperatures and large daily thermal fluctuations. Prior studies have focused on evaluating the physiological response of Atlantic salmon by using stable laboratory-based settings. However, understanding the role of thermal variability on their physiology becomes increasingly important to properly predict their growth and performance in the wild. The objectives of my research were to understand how the growth and performance of parr from the Restigouche River are affected by two different thermal profiles (16-21˚C vs. 19-24˚C) and to compare these responses to parr from the Miramichi River acclimated to the same conditions. After 4 weeks of acclimation to the two distinct thermal profiles, I began measuring length and weight of the fish every month to calculate the growth rate and condition factor. I also conducted a critical thermal maximum (CTmax) test to evaluate thermal tolerance, and an exhaustive swim test to measure swimming performance. I collected blood and tissue samples from control and exercised fish from each treatment to evaluate metabolite profiles. My results suggest that the growth rate was not different between thermal profiles within the Restigouche River, but was lower than the salmon from the Miramichi River. The CTmax was not affected by river origin, but increased in the warmer thermal profile. Moreover, time to exhaustion was not affected by thermal profiles, but it was higher in the Restigouche River. The results show that differences in growth and performance of parr from different river systems exist and this should be taken into account when developing new conservation strategies to maintain healthy populations.