20: Climate Change and the Future of Trout and Char
Ryan Kovach, Bror Jonsson, Nina Jonsson, Ivan Arismendi, Jack E. Williams, Jeffrey L. Kershner, Robert Al-Chokhachy, Ben Letcher, and Clint C. Muhlfeld
Although we often assume trout are highly vulnerable to human activity, they are a remarkably widespread and successful group of fish that now occupy every continent except Antarctica. Their adaptability is exemplified by the wide diversity of aquatic habitats they exploit, ranging from the smallest headwater streams to the oceans. During their evolutionary history salmonid fishes have successfully persisted through dramatic climatic and environmental change (e.g., Waples et al. 2008), and their current distributions span diverse climatic regimes. However, the previous century has produced a sequence of escalating threats to the persistence of trout (Penaluna et al. 2016). Recently, climate change has emerged as a potential tipping point in the conservation and management of trout and char throughout their native and nonnative ranges (Jonsson and Jonsson 2009; Williams et al. 2009; Elliott and Elliott 2010).
Fundamentally, ongoing climate change is concerning because temperature constrains the physiology of all trout and char. Fish cannot live outside their lower and upper incipient lethal temperatures, and somatic growth is restricted to an even narrower temperature range. For instance, Brown Trout Salmo trutta can feed at temperatures down to 0–1°C, but experiments indicate that they do not grow until temperatures reach 4–5°C (Forseth et al. 2009). Growth increases with increasing temperature up to the optimal temperature for growth. In warmer water, growth is constrained by oxygen content (Jonsson and Jonsson 2009; Schulte 2015), and trout begin to die when there is not enough oxygen to sustain their maintenance requirements (Holt and Jørgensen 2015). In the wild, thermal tolerance is lower than the upper incipient lethal level measured in the laboratory (Eaton et al. 1995).