Investigating thermal windows of juvenile sockeye salmon populations in freshwater

There is a general consensus that increasing temperatures have negative impacts on many species of fish. Laboratory studies demonstrate fish growth exhibits a‘thermal window’, increasing with temperature to species-specific thermal optima, beyond which additional increases in temperature lead to decreases in fish growth (Portner et al.2017). Slower growth can result in lower survival, leading to reduced stock productivity.
In British Columbia, annual maximum air temperatures has increased by 0.031°C/year since the 1950s, resulting in increases in the average number of days per year that the Fraser River at Hope is above 19°C from just two days/year in the 1950’s to over 20 days/year in 2010’s (David Patterson. Personal Communication). This increase in water temperature is posing physiological challenges to salmon migration, in some cases inducing pre-spawning mortality (Eliason et al., 2011; Martins et al. 2011).
The influence of climate warming on the growth of juvenile Fraser River Sockeye Salmon rearing in nursery lakes, remains poorly understood, particularly in the context of the multiple factors that regulate growth in these environments. This represents a key area where climate change and other forcings may be influencing stock outcomes (i.e. productivity), unbeknownst to fisheries managers.
We aim to address this knowledge gap by reconstructing stock-specific, long-term time series of annual freshwater growth rates of juvenile Sockeye Salmon in relation to their thermal environments and other key biological and environmental factors.
Scales have long been used to study fish age and growth. The scales of at least eight major Fraser River Sockeye Salmon stocks have been consistently collected by the Pacific Salmon Commission (PSC) since the 1950s, which can be paired with otolith samples since the 1970s.
We propose to non-destructively extract a time series of returning Fraser River Sockeye Salmon (1970 – 2019) freshwater growth from the existing PSC scale archive, and conduct a suite of statistical analyses on these data to define growth variability and change within Fraser River Sockeye Salmon.