Predicting climate change effects on Appalachian trout: Combining GIS and individual-based modeling

We coupled an individual-based model of brook trout (Salvelinus fontinalis) and rainbow trout (Oncorhynchus mykiss) with a geographic information syst em (GIS) database to predict climate change effects on southern Appalachian stream populations. The model tracked individuals of both species through the daily processes of spawning, growth, feeding, mortality, and movement f or 30 years in a stream reach consisting of connected pools, runs, and riff les. The southern Appalachian Plateau was divided into 101 watershed elevat ion band zones. Model simulations were performed for a representative strea m reach of each stream order in each zone. Trout abundance was estimated by multiplying predicted trout densities (measured in number of trout per met er) by the total length of streams of each order in each watershed elevatio n zone. Three climate change scenarios were analyzed: temperature only (1.5 -2.5 degreesC warmer stream temperatures); temperature and how (warmer stre am temperatures and lower baseline flows with threefold higher peak hows); and temperature, flow, and mortality episodes (warmer stream temperatures, changed hows, and flow-related scouring of redds). Increased temperature al one resulted in increased abundances of brook and rainbow trout. The temper ature-and-how scenario resulted in a complex mosaic of positive and negativ e changes in abundances in zones, but little change in total abundance. Add ition of episodic mortality in the form of floods that scour redds and kill eggs and fry caused a net loss of rainbow trout. Predicted changes in habi tat (based on simulation results and temperature alone) were, at best, weak ly correlated with predicted changes in abundance. The coupling of individu al-based models to GIS databases, in order to scale up environmental effect s on individuals to regional population responses, offers a promising appro ach for regional assessments.