The Idiosyncrasies of Streams: Local Variability Mitigates Vulnerability of Trout to Changing Conditions
Andrea Watts

The scientists found that local variability in stream habitat, such as water depth and instream cover, play a greater role in reducing the effects of timber harvest and climate change on trout than previously realized. Instream cover and shade improve trout survival by providing a place to hide from predators.

DISCIPLINE: Fisheries, Hydrology & Water Quality    STUDY: Trask    TYPE: Reports    TAGS: land use, climate change, trout
The role of the geophysical template and environmental regimes in controlling stream-living trout populations
Brooke E. Penaluna, Steve F. Railsback, Jason B. Dunham, Sherri Johnson, Robert E. Bilby, and Arne E. Skaugset

The importance of multiple processes and instream factors to aquatic biota has been explored extensively, but questions remain about how local spatiotemporal variability of aquatic biota is tied to environmental regimes and the geophysical template of streams. We used an individual-based trout model to explore the relative role of the geophysical template versus environmental regimes on biomass of trout (Oncorhynchus clarkii clarkii). We parameterized the model with observed data from each of the four headwater streams (their local geophysical template and environmental regime) and then ran 12 simulations where we replaced environmental regimes (stream temperature, flow, turbidity) of a given stream with values from each neighboring stream while keeping the geophysical template fixed. We also performed single-parameter sensitivity analyses on the model results from each of the four streams. Although our modeled findings show that trout biomass is most responsive to changes in the geophysical template of streams, they also reveal that biomass is restricted by available habitat during seasonal low flow, which is a product of both the stream’s geophysical template and flow regime. Our modeled results suggest that differences in the geophysical template among streams render trout more or less sensitive to environmental change, emphasizing the importance of local fish–habitat relationships in streams.

DISCIPLINE: Fisheries    STUDY: Trask    TYPE: Journal Articles    TAGS: geophysical template, environmental regimes, trout
Local Variability Mediates Vulnerability of Trout Populations to Land Use and Climate Change
Brooke E. Penaluna, Jason B. Dunham, Steve F. Railsback, Ivan Arismendi, Sherri L. Johnson, Robert E. Bilby, Mohammad Safeeq, Arne E. Skaugset

Land use and climate change occur simultaneously around the globe. Fully understanding their separate and combined effects requires a mechanistic understanding at the local scale where their effects are ultimately realized. Here we applied an individual-based model of fish population dynamics to evaluate the role of local stream variability in modifying responses of Coastal Cutthroat Trout (Oncorhynchus clarkii clarkii) to scenarios simulating identical changes in temperature and stream flows linked to forest harvest, climate change, and their combined effects over six decades. We parameterized the model for four neighboring streams located in a forested headwater catchment in northwestern Oregon, USA with multi-year, daily measurements of stream temperature, flow, and turbidity (2007– 2011), and field measurements of both instream habitat structure and three years of annual trout population estimates. Model simulations revealed that variability in habitat conditions
among streams (depth, available habitat) mediated the effects of forest harvest and climate change. Net effects for most simulated trout responses were different from or less than the sum of their separate scenarios. In some cases, forest harvest countered the effects of climate change through increased summer flow. Climate change most strongly influenced trout (earlier fry emergence, reductions in biomass of older trout, increased biomass of young-of-year), but these changes did not consistently translate into reductions in biomass over time. Forest harvest, in contrast, produced fewer and less consistent responses in trout. Earlier fry emergence driven by climate change was the most consistent simulated response, whereas survival, growth, and biomass were inconsistent. Overall our findings indicate a host of local processes can strongly influence how populations respond to broad scale effects of land use and climate change.

DISCIPLINE: Fisheries    STUDY: Trask    TYPE: Journal Articles    TAGS: trout, land use, climate change
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