Effects of spatial extent on modeled relations between habitat and anadromous salmonid spawning success

Abstract

We address the question of spatial extent: how model results depend on the amount and type of space represented. For models of how stream habitat affects fish populations, how do the amount and characteristics of habitat represented in the model affect its results and how well do those results represent the whole stream? Our analysis used inSalmo, an individual-based model of anadromous salmonid spawning, incubation, and juvenile rearing. The model was applied to 12 sites, totaling 4.0 km in length, on Clear Creek, California, treating the simulated 4.0 km as a synthetic whole stream. Simulation experiments examined responses of anadromous salmonid spawning and rearing success to habitat variables, such as flow and temperature, when the model included each individual site, all sites, and random combinations of two to nine sites. Some responses, such as temperature effects on egg incubation, were insensitive to spatial extent. Other responses, including the effects of flow on the production of large juveniles, varied sharply among sites and varied with spatial extent. Most small sites had little effect on overall results, but one small site provided exceptionally good juvenile rearing habitat and strongly affected the responses of the entire stream. Larger sites (length > 15 channel widths) in distinct habitat types (e.g., highly disturbed and recently restored) also had strong effects. Including more or longer sites generally increased model representativeness but not consistently. Results highly representative of the entire stream could also be obtained by combining large sites in typical habitat with “hot spots” of especially productive habitat. Finally, sites lower in the watershed appear to be more important to model results and anadromous salmonid spawning success because more juveniles migrate through them.

Citation

Railsback, Steven F.; Harvey, Bret C.; White, Jason L. 2015. Effects of spatial extent on modeled relations between habitat and anadromous salmonid spawning success. Transactions of the American Fisheries Society. 144(6): 1220-1236.