Effects of Temperature Fluctuation on Burbot Embryos: Implications of Hydropower and Climate Change

Populations of Burbot Lota lota across the Holarctic ecozone are facing imperilment from environmental warming, particularly in ecosystems impacted by hydropower and climate change. We conducted a series of laboratory experiments to evaluate the tolerance of Burbot embryos to various thermal regimes. Both cyclical and constant warming between 4.0°C and 5.5°C during the initial 25 degree‐days of embryo development led to significant deformity and mortality of protolarvae, with faster rates of temperature increase (i.e., 0.4°C/d) causing greater harm than gradual rates of warming. Random family effects interacted with incubation temperature of embryos to account for significant variability in deformity and survival of protolarvae. These findings have management implications for identifying and/or augmenting the thermal fitness of populations in modified ecosystems, particularly in Burbot populations where aquaculture production supports abundance. A model of hatching time based on degree‐days of embryo development was also developed to improve predictions of natural emergence, peak larvae abundance, and optimal timing for larvae stocking. It is recommended that hydropower operations avoid thermopeaking during winter spawning of Burbot, especially if reservoir discharges exceed 4°C. Maintaining water temperatures below 3°C for at least the first 2 weeks of embryogenesis is critical for Burbot reproduction and underscores the importance of ice‐covered spawning habitats. Global climate trends are expected to exacerbate warming in rivers, and many challenges lie ahead for conservation efforts seeking to mitigate the risks of Burbot extirpation.