From coastal shores to inland mountains, salmon are part of the fabric of Alaska. Salmon have been harvested by Alaska Natives for thousands of years and remain a critical part of the state’s commercial, recreational and subsistence fisheries. As anadromous fish, salmon spend the first months to years of their lives in freshwater before migrating to the ocean and later returning to freshwater to spawn. As climate continues to change in Alaska, so will the characteristics of the state’s freshwater streams. In Southeast Alaska, climatologists are predicting increasing air temperatures and annual rain accumulation, and decreasing precipitation falling as snow—changes that will affect freshwater salmon habitat. An Alaska Sea Grant-funded research project is assessing how the impacts of climate change on Southeast Alaska rivers and stream may affect salmon productivity.

The research is a collaboration between Jeffrey Falke with U.S. Geological Survey and University of Alaska Fairbanks (UAF), Ryan Bellmore with U.S. Forest Service, Rebecca Bellmore with Southeast Alaska Watershed Coalition, Davin Holen with Alaska Sea Grant, and Chris Sergeant, a doctoral student at the University of Alaska Fairbanks, College of Fisheries and Ocean Sciences.

The research team is examining the effects of changes in two key habitat characteristics—stream flow and water temperature—to understand how climate change may affect freshwater salmon life cycles.

Stream flow—the amount of water moving through the stream—and water temperature can greatly affect growth rates, behavior, and even survival of salmon from adults returning to rivers to spawn. These factors can also affect eggs incubating in stream gravels and juveniles that rear in freshwater before migrating to the ocean. For example, flood events can scour eggs from the stream bed, whereas low flows—particularly those that occur in the summer—can result in die-offs of adult spawning salmon. Warmer water temperatures can accelerate egg development and change the metabolism of juvenile salmon. If adequate food is available, salmon can grow faster in warmer water.

The research team is using data from the Southeast Alaska Stream Temperature Monitoring Network, a group of organizations collectively monitoring water temperature in more than 50 watersheds in the region.

“This project will be the first to use data from the monitoring network to understand how our salmon may be affected by climate change, and our partners are really excited about it,” said Rebecca Bellmore.

The team in turn supports the Southeast Alaska Stream Monitoring Network through continued maintenance of some temperature data loggers within the network and field trainings for new partners. The loggers record stream temperature hourly throughout the year and require in-person checkups twice a year. Some of the sites have been monitored for over ten years, while others have only recently been added to the network.

The hydrologically-diverse environment of Southeast Alaska is characterized by three main stream types, each with different flow and temperature regimes. Glacial-fed streams are marked by high flow in the summer, but relatively stable stream temperature throughout the year. Snowmelt-fed streams have peaks of higher flow in the spring and fall and higher stream temperature in late summer. Rainfall-fed streams have higher flow in the winter and fall months and higher stream temperatures in the summer. As the region warms and receives less snow and more rain in the future, the dominant flow patterns that historically characterized streams are expected to change, which will affect their local salmon populations. Currently, there are only a handful of streams in Southeast Alaska where water flow, or the volume of water discharge, is measured on a continuous basis.

“Because field data are so sparse, we have to turn to other methods to estimate stream flow for many locations,” said Bellmore.

For these, the team will be using modeled stream flow data that accounts for rain, snow, and glacier melt that was developed for the Gulf of Alaska (Beamer et al 2016).

The water flow and temperature data are used in the salmon productivity model aimed at estimating salmon productivity in Southeast Alaska streams in a changing climate. The salmon productivity model looks at how stream temperature and flow affect salmon productivity, with a focus on coho salmon (Oncorhynchus kisutch), chum salmon (O. keta), and pink salmon (O. gorbuscha). Assessing effects of stream changes across all the salmon freshwater life stages will better account for cumulative effects. Additionally, these effects can be specific to the type of stream. For example, the magnitude of temperature changes may be lower in glacial-fed streams than rainfall-fed streams.

As the team finalizes the salmon productivity model, they are working with local communities to develop a user-friendly interface for Southeast Alaska communities and subsistence harvesters. Across many rural communities in Southeast Alaska, access to salmon may be highly localized and available in a handful of streams. The salmon productivity model is aimed at providing future scenarios for local salmon populations as a tool to help communities better plan for a changing climate landscape.

UAF graduate student Chris Sergeant talks about his Ph.D. project.

More information on this research can be found at the project page Assessing the resilience of southeast Alaskan salmon to a shifting freshwater environment.

–Written by Maggie Chan.

References

Beamer, J. P., Hill, D. F., Arendt, A., & Liston, G. E. (2016). High‐resolution modeling of coastal freshwater discharge and glacier mass balance in the Gulf of Alaska watershed, Water Resources Research, 52(5), 3888– 3909, doi:10.1002/2015WR018457.

Edwards, R.T., D’Amore, D.V., Norberg, E., & Biles, F. (2013). Riparian ecology, climate change and management in North Pacific coastal rainforests. In G.H. Orians & J.W. Schoen (Eds.)North Pacific Temperate Rainforests: Ecology & Conservation (pp. 43-72). Seattle, WA: Nature Conservancy of Alaska, University of Washington Press, Audubon Alaska.