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

Abstract

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.

Triploid burbot, Lota lota, production: Optimization of thermal and hydrostatic parameters, tetraploid induction, and confirmation of triploid sterility

“…At the conclusion of each experiment, each batch of eggs was volumetrically quantified using a graduated cylinder, after settling for 3 min, then transferred to a 1.27-cm diameter 10 mL experimental incubation chamber. Each chamber was placed, randomly, into a single mass pneumatic-drive incubator system using a shared water bath until hatch (Ashton et al, 2021). Incubation chambers were checked daily, dead eggs were removed, and temperature was monitored.…”

Otolith 87Sr/86Sr identifies natal origin, movement and life history of Burbot Lota lota in the Kootenai River following 45 years of impoundment

“…Winter water level fluctuations in reservoirs, for instance, can reduce reproductive success through dewatering or by limiting access to littoral or tributary spawning grounds (Gaboury & Patalas, 1984; Wilcox & Meeker, 1992). Moreover, for winter spawning species such as Burbot Lota lota , thermal stress from the discharge of warmer hypolimnetic water during early embryonic development can potentially reduce larval recruitment due to increased deformity and mortality at hatch (Ashton et al, 2021).…”

“…Burbot also have highly specific thermal requirements for reproduction and embryonic development (Ashton et al, 2019; Harrison et al, 2016). Successful spawning and egg survival occur during the late winter and are closely linked to temperatures less than 4°C (Ashton et al, 2021). Impoundments that alter this thermal profile, impair spawning migration or dewater littoral spawning habitat and thus have the potential to negatively influence reproductive success and larval recruitment (Paragamian et al, 2005; Stapanian et al, 2010).…”