Pacific Salmon in Hot Water: Applying Aerobic Scope Models and Biotelemetry to Predict the Success of Spawning Migrations

Abstract

Concern over global climate change is widespread, but quantifying relationships between temperature change and animal fitness has been a challenge for scientists. Our approach to this challenge was to study migratory Pacific salmon (Oncorhynchus spp.), fish whose lifetime fitness hinges on a once-in-a-lifetime river migration to natal spawning grounds. Here, we suggest that their thermal optimum for aerobic scope is adaptive for river migration at the population level. We base this suggestion on several lines of evidence. The theoretical line of evidence comes from a direct association between the temperature optimum for aerobic metabolic scope and the temperatures historically experienced by three Fraser River salmon populations during their river migration. This close association was then used to predict that the occurrence of a period of anomalously high river temperatures in 2004 led to a complete collapse of aerobic scope during river migration for a portion of one of the sockeye salmon (Oncorhynchus nerka) populations. This prediction was corroborated with empirical data from our biotelemetry studies, which tracked the migration of individual sockeye salmon in the Fraser River and revealed that the success of river migration for the same sockeye population was temperature dependent. Therefore, we suggest that collapse of aerobic scope was an important mechanism to explain the high salmon mortality observed during their migration. Consequently, models based on thermal optima for aerobic scope for ectothermic animals should improve predictions of population fitness under future climate scenarios.

Effects of climate change on fish reproduction and early life history stages

“…In addition to acclimatory responses owing to thermal exposure history, individuals within a population can exhibit different thermal preferences (i.e. individual genetic variability), and different populations can be locally adapted to different thermal regimes (Crawshaw and O'Connor 1997;Farrell et al 2008;Munday et al 2008a). This variation provides the raw material for selection of genotypes that are more tolerant.…”

Variation in Metabolic Rate among Individuals Is Related to Tissue-Specific Differences in Mitochondrial Leak Respiration

“…Therefore, AS may have a significant impact on fitness but displays significant intraspecific variation (Farrell et al 2008;Sandblom et al 2014;Auer et al 2015aAuer et al , 2015c; but see Norin et al 2014). Both minimum and maximum metabolic rate are responsible for intraspecific variation in AS since they exhibit consistent differences among individuals over extended periods of time, even within a population under standardized conditions Burton et al 2011;Swanson et al 2012;Careau et al 2014aCareau et al , 2014bGifford et al 2014).…”

Indirect genetic effects underlie oxygen-limited thermal tolerance within a coastal population of chinook salmon

“…Aerobic scope is thereby reduced until an upper critical temperature (T crit ) is reached, above which an animal's capacity for aerobic activity cannot exceed routine rates. Because of the lack of oxygen available for aerobic metabolism above routine needs, such loss of scope reduces the capacity for growth, reproduction and aerobic swimming, which can lead to reduced survival [19,20].…”