Growing pains? SFU research tracks 100 years of salmon adaptation to climate change

Juvenile salmon in British Columbia are growing larger than they did 100 years ago due to climate change, according to a new Simon Fraser University-led study.

Century-old fish scales are yielding new insights into how salmon populations are responding to climate change in northern B.C., and how maintaining the integrity of freshwater habitats may help salmon adapt to warming temperatures.

SFU biological sciences Liber Ero Postdoctoral Fellow Michael Price, with other SFU researchers and Fisheries and Oceans Canada, have used modern genetic tools to analyze fish scales collected from fisheries since 1913 to reconstruct the historical growth of juvenile sockeye in various lakes across the Skeena watershed.

Their paper, published in Global Change Biology, finds that the annual freshwater growth of juvenile salmon is substantially higher in recent years than it was a century ago, by about 35 per cent.

They also found that while the annual growth of juvenile sockeye has increased for nearly all populations, fish from relatively deep lakes are growing faster than ones from shallow lakes.

“Particular lake habitats play an important role in modulating the effect of high summer temperatures, resulting in enhanced growth of these important fishes,” says Price.

As cold water fishes, salmon are sensitive to warming temperatures.

Price explains that warmer temperatures in lakes can help fish grow faster both by increasing their metabolism, which can help them capture more prey, and by increasing the amount of food production in those habitats.

But this is only true up to a point. When water temperatures are higher than salmon’s “thermal niche” they can become stressed and fail to thrive.

The authors note that while climate data indicates that ambient air temperature is similar across the watershed, deeper lakes do not warm as quickly as shallow lakes. As temperatures become too warm at the lakes’ surface, deeper water can provide a cool refuge for juvenile salmon.

As a result, relatively deep and characteristically cold nursery lakes once considered poor producers of salmon now appear to be increasing in their importance. Fish in these habitats are likely to thrive in the near term under forecasted climate change.

Price says that maintaining the integrity of a variety of freshwater habitats will help foster a diverse climate response portfolio for important fish species, which in turn can ensure that salmon watersheds are resilient to future environmental change.

“Our work suggests that habitat diversity provides a spectrum of opportunities for salmon to adapt to future increases in temperature associated with climate change,” says Price.