Time to Evolve? Potential Evolutionary Responses of Fraser River Sockeye Salmon to Climate Change and Effects on Persistence

Abstract

Evolutionary adaptation affects demographic resilience to climate change but few studies have attempted to project changes in selective pressures or quantify impacts of trait responses on population dynamics and extinction risk. We used a novel individual-based model to explore potential evolutionary changes in migration timing and the consequences for population persistence in sockeye salmon Oncorhynchus nerka in the Fraser River, Canada, under scenarios of future climate warming. Adult sockeye salmon are highly sensitive to increases in water temperature during their arduous upriver migration, raising concerns about the fate of these ecologically, culturally, and commercially important fish in a warmer future. Our results suggest that evolution of upriver migration timing could allow these salmon to avoid increasingly frequent stressful temperatures, with the odds of population persistence increasing in proportion to the trait heritability and phenotypic variance. With a simulated 2°C increase in average summer river temperatures by 2100, adult migration timing from the ocean to the river advanced by ∼10 days when the heritability was 0.5, while the risk of quasi-extinction was only 17% of that faced by populations with zero evolutionary potential (i.e., heritability fixed at zero). The rates of evolution required to maintain persistence under simulated scenarios of moderate to rapid warming are plausible based on estimated heritabilities and rates of microevolution of timing traits in salmon and related species, although further empirical work is required to assess potential genetic and ecophysiological constraints on phenological adaptation. These results highlight the benefits to salmon management of maintaining evolutionary potential within populations, in addition to conserving key habitats and minimizing additional stressors where possible, as a means to build resilience to ongoing climate change. More generally, they demonstrate the importance and feasibility of considering evolutionary processes, in addition to ecology and demography, when projecting population responses to environmental change.

Aerobic scope increases throughout an ecologically relevant temperature range in coho salmon

“…are icons of the Pacific Northwest of North America and utilize aquatic environments that are diverse across life stages, populations and species (Quinn, 2005). During their migration from the Pacific Ocean to freshwater spawning grounds, maturing adult salmon sometimes face extreme environmental challenges (Reed et al, 2011). While there is some evidence that Pacific salmon can temporarily delay river entry or otherwise alter their migration behaviour to avoid extreme conditions (Goniea et al, 2006;Mantua et al, 2015), in most cases salmon make their migration towards their natal freshwater locale on a relatively fixed schedule (Crozier et al, 2008) and represent a classic example of local adaptation (Wright, 1978).…”

“…Indeed, a progressive decline in AS above historic modal river temperatures has been proposed as one of several potential mechanisms for population-specific en route mortality at high temperatures Hinch et al, 2012). With climatic change occurring at an alarming rate and regarded as a key pressure acting upon Pacific salmon conservation and management (Patterson et al, 2007;Crozier et al, 2008;Bryant, 2009;Martins et al, 2011;Reed et al, 2011), AS has emerged as a potentially useful functional measurement with which to make predictions about the thermal niche of aquatic ectotherms and hence potential fitness outcomes under future warming scenarios.…”

Summer temperature regimes in southcentral Alaska streams: watershed drivers of variation and potential implications for Pacific salmon

“…However, targeted management strategies can increase resilience in aquatic ecosystems to a changing climate, such as improving riparian vegetation to shade streams, restoring fish passage to provide access to thermal refugia, and identifying sensitive areas for conservation Isaak et al 2010). These strategies, in addition to maintaining habitat connectivity and complexity, along with salmon's inherent life history diversity and evolutionary potential, will help the long-term viability of the region's salmon populations (Hilborn et al 2003;Crozier et al 2008;Schindler et al 2010;Reed et al 2011).…”

Sperm in hot water: Direct and indirect thermal challenges interact to impact on brown trout sperm quality

“…Freshwater species face particularly acute challenges because of the cumulative effects of climate change and other anthropogenic stressors such as habitat modifications, pollution and over-exploitation, threatening their ecosystems (IPCC, 2014). Climate change-induced decreases in suitable thermal habitats for freshwater species are already evident (Hari et al, 2006;Wenger et al, 2011a,b), forcing species to adapt or relocate in order to persist (Isaak et al, 2011;Reed et al, 2011). This is especially crucial for ectothermic species with complex life histories, such as migratory fish (Crozier et al, 2008).…”