Simulated juvenile salmon growth and phenology respond to altered thermal regimes and stream network shape
Fullerton, A., B. Burke, J. Lawler, C. Torgersen, Joe Ebersole, AND S. Leibowitz. Simulated juvenile salmon growth and phenology respond to altered thermal regimes and stream network shape. Ecosphere. ESA Journals, 8(12):e02052, (2017).
Warming of streams poses a significant threat to cold-water fish like salmon. But streams and rivers are naturally thermally diverse, and effects of climate change or human activities that warm streams will not be uniform across stream networks. Additionally, fish like salmon move within streams and rivers, often over significant distances over which conditions will vary. Because of the diversity of temperatures and the complexity of fish movement, predicting the effects of water temperature changes on fish can be difficult. Use of modeling simulations can help understand effects of interactions between fish movement and spatially-variable temperatures. This research used an individual-based modeling approach to assess potential outcomes for fish given a variety of temperature patterns within stream networks. The results indicate that fish growth is highly sensitive not only to the overall change in temperature, but also the spatial pattern of those temperatures. Growth increases where fish were able to find temperatures matching optimal growth requirements, and decreased where temperatures were cooler or warmer than optimum. This response varied depending on the spatial arrangement of temperature within stream networks. Having access to a variety of streams with different topologies and associated thermal patterns can promote diversity in salmon life history strategies, and may enable persistence and resilience as the climate changes. Our work adds to a growing body of literature demonstrating that spatiotemporal context and stream network relationships are important to salmon and should be explicitly considered during conservation and climate adaptation planning. This paper contributes to SSWR 3.01C
Context. Thermally diverse habitats may afford fish protection from climate change by providing opportunities to behaviorally optimize growing conditions. However, it is unclear what role the spatial properties of river networks will play in determining risk. Objectives. We hypothesized that climate-altered thermal regimes will change growth and timing of life history events such as hatching or migration; but that changes will be moderated in topologically complex stream networks where opportunities to thermoregulate are high. Methods. We developed a spatially-structured, individual-based model for Chinook salmon (Oncorhynchus tshawytscha) in which movement decisions and growth were governed by water temperature and conspecific density. We evaluated growth and phenology under six thermal regime scenarios (each having a different maximum, rate of warming, and variability) in three network shapes of increasing spatial complexity. Results. In a cool thermal scenario, salmon grew best and were capable of smolting earliest in the network having the lowest spatial complexity. In warmer scenarios, fish grew best and could smolt earliest in the stream network with the most complex spatial configuration, where water temperatures experienced by fish were ~2°C closer to optimal temperatures for growing. Changes in growth were positive and large given warmer summer maxima, positive and small given earlier spring warming, and negative and small given variable thermal regimes.Conclusions. Our results demonstrate that network topology may influence how fish respond to future thermal landscapes, and should help conservation planners incorporate a spatiotemporal context into decisions that will promote long-term viability of salmon given climate change.