Climate change and geomorphic evolution in an Alaskan watershed and implications for salmon production
Griffiths, Jennifer Rhiannon
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Freshwater ecosystems are not only the source of a disproportionate number of ecosystem services given their relative area on the planet, but they are also highly sensitive to anthropogenic impacts including climate change. Landscape heterogeneity provides a filter for regional climate forcing in aquatic systems and provides the context in which the biological components of ecosystems will interact with climate change. I used the Chignik watershed, Alaska as a case study in which to explore the response of juvenile sockeye salmon (Oncorhynchus nerka) growth and body condition to differences across habitats and variation in climate. Furthermore, I investigated the interaction of climate change and geomorphic evolution and its effects on juvenile sockeye salmon habitat and growth. I used genetic tools to assess individual performance of sockeye salmon among connected freshwater habitats. I found that individual performance converged on habitat productivity rather than being determined by genetic origin. I investigated the effects of climate variability on juvenile salmon growth among lake habitats using 40 years of freshwater growth data from scales. Growth showed a coherent response to climate variables affecting growing season duration but opposing responses to growing season temperatures. This indicated that different lake habitats not only filter regional climate differently but that this leads to differences in the biological response. Juvenile sockeye salmon length data over a similar timeframe indicated that temperature had a greater effect on growth than sockeye density. Finally, I assessed the relative importance of air temperature, lake volume and tributary for lake thermal regimes and juvenile sockeye salmon growth. Increases in lake volume had little effect on lake thermal regimes which were highly sensitive to lake temperature. Future increases in air temperature will likely reduce growth of juvenile sockeye although maintaining tributary connectivity is important to reducing the effects of air temperature. Because uncertainty exists in how freshwater ecosystems will respond to climate change preserving networks of heterogeneous habitat may be critical to supporting ecosystem resilience. Intact ecosystems provide an opportunity to evaluate the relative importance of climate, geomorphology and connectivity for salmon populations and inform the management and restoration of impacted landscapes.
- Fisheries