Assessing Freshwater Climate Indicators and Salmon Vulnerability to Climate Change
Climate change and Pacific salmon
Climate change is one of the most pressing risks to Pacific salmon populations and their habitats. The effects of climate change are felt by salmon at every stage of their life cycle. In freshwater, increasing stream temperatures reduce migration success of spawners and increase their susceptibility to disease. Extreme weather events can lead to floods that flush out incubating eggs, while reduced summer flows limit available habitat for populations that rear in freshwater. These direct effects are compounded by landscape changes resulting from both climate change and other anthropogenic disturbances that affect freshwater habitats, such as deforestation from fires, mountain pine beetle, and logging. In the ocean, increasing sea temperatures and shifting currents are changing marine food webs, affecting the abundance and diversity of forage species upon which salmon rely.
However, not all salmon populations are equally vulnerable to the impacts of climate change. To date, salmon populations in the southern part of British Columbia – where temperatures and human population density are the highest – seem to have been most affected by climate change. However, climate projections suggest that future warming may be greatest in northern Canada. In addition to different timelines and magnitude of climate change impacts, the incredible life-history diversity of salmon means that there is also variability among populations in their sensitivity and adaptability. For example, pink and chum salmon that spend less time rearing in freshwater may be less sensitive to warming streams than species that undertake long freshwater migrations and/or rear in lakes, such as sockeye. Prioritizing strategies for mitigating climate-related pressures or enhancing the resilience of salmon Conservation Units (CUs)* to climate change requires consideration of the variability in exposure, sensitivity, and adaptability among CUs.
Over the past 5 years, the PSF has been expanding and refining the Pacific Salmon Explorer (www.salmonexplorer.ca), an interactive data visualization tool for tracking and reporting information on the status of Pacific salmon CUs and their freshwater habitats. However, information on current and future impacts of climate change remain conspicuously absent from the Pacific Salmon Explorer, and including information on climate change is the most common request received from end users. This multi-year project, funded through a grant from the British Columbia Salmon Restoration and Innovation Fund, will incorporate climate indicators and climate vulnerability assessments into the Pacific Salmon Explorer.
Climate indicators for salmon habitats
Our first step is identifying appropriate climate indicators that reflect how salmon habitats are changing in response to climate change. There are many environmental variables that are being affected by climate change, and almost all are related in one way or another. For example, warmer temperatures are melting glaciers and changing the hydrology of freshwater ecosystems, often leading to earlier peak flows, reduced summer flows, and warmer stream temperatures. In the Pacific Salmon Explorer, we aim to include indicators that are directly relevant to Pacific salmon survival. Work is underway to identify and compile datasets that can inform indicators of stream temperature and flow – two important variables that influence the quality and quantity of freshwater spawning, rearing, and migratory habitats – as well as relevant marine indicators, such as sea surface temperature.
Climate vulnerability framework for Pacific salmon
The vulnerability of Pacific salmon CUs to climate change will depend on their exposure to climate-related habitat impacts, as captured by the climate indicators we are compiling, but also on their sensitivity to these changes and their capacity to adapt. Climate vulnerability assessments of salmon in the US (e.g., Crozier et al. 2019) have relied on expert elicitation to quantify the sensitivity and adaptability of salmon populations to climate change. We aim to build on those studies by developing a made-in-BC approach to assessing vulnerability that is quantitative, data-driven, and broadly applicable – as we have done in our assessments of habitat and biological status in the Pacific Salmon Explorer.
Climate indicators and the outcome of vulnerability assessments will be publicly available through the Pacific Salmon Explorer, with supporting technical documentation detailing the data and methods applied. Providing information on the status and trends of salmon and their habitats through the lens of a changing climate will help decision-makers better understand the current extent and intensity of climate pressures on salmon, the relative vulnerability of salmon CUs to future climate pressures, and prioritize strategies for mitigating these pressures or enhancing the resilience of salmon CUs to climate change.
- State of the Canadian Pacific Salmon: Responses to Changing Climate and Habitats (2019). Available from https://waves-vagues.dfo-mpo.gc.ca/Library/40807071.pdf
- PSF Climate Adaptation Workshop (April 2021). Recordings available at https://www.youtube.com/channel/UCb1DgitSa_86ylR5CZlFe1A
- Assessing Freshwater Climate Indicators and Salmon Vulnerability to Climate Change: Year 1 Update (2021 – 2022)
* Conservation Units (CUs) are genetically and geographically distinct populations of wild salmon. These groups of fish are sufficiently unique that, if extirpated, are unlikely to recolonize within a human lifetime.