Mapping the Unknown: Modeling Future Scenarios of Riverine Fish Communities

Riverscapes can be defined by spatial and temporal variation in a suite of environmental conditions that influence the distribution and persistence of riverine fish populations.  Fish in riverscapes can exhibit extensive movements, require seasonally-distinct habitats for spawning and rearing, and respond to both environmental and biotic pressures.  These factors pose substantial challenges to fish population modeling. Here we present a modeling approach for simulating assemblages of fish in riverine landscapes. The approach allows a user to determine the grain and extent of river networks within which fish populations reproduce, move, and survive in response to both environmental drivers and assemblage interactions. We apply the model to a fish assemblage in the Willamette River basin of Oregon, a region where human population and water demand are expected to grow substantially over the next 50 years. By explicitly defining fish population responses to environmental factors such as streamflow and temperature, and interaction weights accounting for predation and competition, the approach provides a heuristic tool for identifying critical data gaps for projecting the effects of future landscape scenarios on fish assemblages.  Initial results provide testable hypotheses regarding species distributions within the basin and projected responses to climate change and hydropower management.  The tool also provides a rich opportunity to further test theory implicit within the riverscape view of fish populations.