Forecasting the interactive effects of climate change, riparian land use and invasive species on Pacific salmon
Climate change, increasing agricultural and urban land-use, and invasive species threaten the functioning of freshwater ecosystems in the Pacific Northwest. Resource managers, scientists and policy makers are becoming increasingly cognizant that the future will witness simultaneous changes in these factors, yet we still lack the science and decision-support tools required to develop management strategies that are robust to future environmental change. Today, elevated stream temperature is one of the most pervasive water quality issues in the Pacific Northwest, and projected climate change and riparian vegetation loss will only exacerbate this problem. Rising temperatures have obvious and direct implications for native cold-water salmonids, but will also alter the composition of aquatic biota by facilitating the range expansion of cool- and warm-water invasive species, including invasive smallmouth bass (Micropterus dolomieu) which impact salmon (Carey et al. 2011). Quantifying where, when, and to what degree temperature-mediated invasions are likely to occur in the Pacific Northwest in response to climate and land-use change is critical to predicting and mitigating the future impacts of these large-scale drivers.
APPROACH AND RESULTS
This research project – led by faculty (Olden, Lawler, Torgersen) and graduate students in the School of Aquatic and Fishery Sciences and School of Environmental and Forestry Sciences – applies an analytical framework that links climate change, riparian land-use, stream thermodynamics, and species invasions for the management and conservation of native salmonids (Figure 1). The framework is being applied to the John Day River, Oregon, where human-induced stream warming is promoting the range expansion of invasive smallmouth bass (Micropterus dolomieu) and northern pikeminnow (Ptychocheilus oregonensis) into formerly cool reaches that contain critical habitats for endangered spring-run Chinook salmon (Oncorhynchus tshawytscha) (Lawrence et al. 2012). The project has three objectives: (1) predict spatiotemporal patterns of riverine thermal regimes in response to future climate change, geomorphic sensitivity, and riparian land-use; (2) forecast species-specific responses to projected future thermal regimes; (3) evaluate alternative scenarios of climate change to identify critical opportunities for riparian restoration (i.e., riparian fencing) and protection efforts (i.e., conservation easements) to mediate future climate-induced warming of streams and species invasions.
For a moderate end-of-century climate change scenario, we estimate declines in the volume of habitat in the John Day River (Oregon) for Chinook salmon, rainbow trout, and bull trout as 69–95%, 51–87%, and 86–100%, respectively (Ruesch et al. 2012, Figure 2). Although some restoration strategies may be able to offset these projected impacts, our forecasts point to how and where restoration and management efforts might focus. By contrast, we documented the upstream intrusion of smallmouth bass into salmon rearing grounds of the north fork John Day River (Lawrence et al. 2012). This is especially problematic because juvenile Chinook don’t recognize bass as predators (Kuehne and Olden 2012), an oversight likely resulting from an unshared evolutionary history between predator and prey. Experiments in artificial stream channels showed that warmer temperatures result in significantly stronger and more variable antipredator responses (surface shoaling and swimming activity) of juvenile Chinook salmon to smallmouth bass, while physiological indicators (plasma glucose, plasma cortisol) suggest suppression of physiological mechanisms in response to the combined stressors. These patterns corresponded with additive negative growth in predation, temperature, and combined treatments (Kuehne et al. 2012). In summary, this project is among the first to investigate the interrelated roles of climate change and riparian land-use in promoting the spread and impact of invasive species in stream ecosystems.
Carey, M.P., Sanderson, B.L., Friesen, T.A., Barnas, K.A. and J.D. Olden. 2011. Smallmouth bass in the Pacific Northwest: A threat to native species; a benefit for anglers. Reviews in Fisheries Science 19:305-315.
Kuehne, L.M., and J.D. Olden. 2012. Prey naivety in the behavioural responses of juvenile Chinook (Oncorhynchus tshawytscha) salmon to an invasive predator. Freshwater Biology 57: 1126-1137.
Kuehne, L.M., Olden, J.D., and J.J. Duda. 2012. Costs of living for juvenile Chinook salmon in an increasingly warming and invaded world. Canadian Journal of Fisheries and Aquatic Sciences 69: 1621-1630.
Lawrence, D.J., Olden, J.D., and C.E. Torgersen. 2012. Spatiotemporal patterns and habitat associations of smallmouth bass (Micropterus dolomieu) invading salmon-rearing habitat. Freshwater Biology 57: 1929-1946.
Ruesch, A.S., Torgersen, C.E., Lawler, J.J., Olden, J.D., Peterson, E.E., Volk, C.J., and D.J. Lawrence. 2012. Projected climate-induced habitat loss for salmonids based on a network model of stream temperature. Conservation Biology 5:873-882.
Julian Olden (School of Aquatic and Fishery Sciences, University of Washington) email@example.com