Cooperative Fish and Wildlife Research Units Program: all
Education, Research and Technical Assistance for Managing Our Natural Resources

In the northern latitudes of western North America, climate change is altering patterns of streamflow and water temperature via elevated air temperature, increased frequency and intensity of rainfall, and glacier retreat. The subsequent increases in stream temperature, flooding, and drought can alter the population dynamics of culturally and economically important aquatic species such as Pacific salmon (Oncorhynchus spp.). Modeling approaches designed to assess the vulnerability of salmon to climate change tend to focus on average environmental conditions and typically do not account for extreme events lasting days to weeks. To explore how these short-duration disturbances impact salmon populations, we developed a life cycle model that mechanistically links coho salmon (O. kisutch) abundance to daily streamflow and thermal regimes. Model design was motivated by two questions: 1) how does coho salmon abundance respond to short-duration floods, droughts, and elevated water temperatures in glacier-, snow-, and rain-fed streams? 2) How does the temporal resolution of streamflow and water temperature data influence modeled abundance? In our simulations, salmon populations in rain-fed streams were the most sensitive to winter floods that increased egg mortality and drought conditions that concentrated juvenile salmon in warm, isolated pools. Salmon populations in similarly sized snow- and glacier-fed streams were relatively resilient to all but the most extreme flood and drought scenarios. These findings suggest that salmon abundance in the thousands of rain-fed streams draining to coastal Alaska and British Columbia may become more variable year-to-year depending on the future frequency and severity of winter floods and summer droughts. Aggregating streamflow and temperature time series from daily into weekly and monthly averages dampened the influence of extreme events and predicted impacts on populations. Our model can be adapted to additional climate change scenario planning exercises for any salmonid-bearing stream with sufficient measurements of habitat characteristics, streamflow, and water temperature.