Recovery plans for Pacific salmon listed under the US Endangered Species Act often rely on information on historical habitat suitability data as both a template against which current status is evaluated and a guide for setting future recovery goals. However, data on historical habitat suitability are difficult, if not impossible, to obtain over areas large enough to be relevant for recovery planning. Thus, models are needed that can estimate the potential of streams to provide suitable habitat for salmon. To address this need, biologists have developed simple, expert-opinion models (termed “Intrinsic Potential” (IP) models) utilizing remotely-collected spatial data and geographical information systems to estimate habitat suitability for salmonid species. These IP models use a small number of habitat parameters that are resistant to change from anthropogenic activities and that capture the geomorphic characteristics constraining suitability of habitat for fish. Here we develop and evaluate an IP model for spawning habitat of Lower Columbia River Fall Chinook salmon. The model uses three parameters: 1) reach width, 2) valley confinement (ratio of reach width to valley width), and 3) reach gradient. With this model, we estimate habitat suitability for each reach of stream accessible to Fall Chinook in the Lower Columbia River basin. To calculate the amount of suitable habitat available to each Fall Chinook population, we multiply the suitability score for each reach by its length and sum these products for all reaches in the population.
We map reach suitability scores to locate clusters of habitat with high potential to support spawning Fall Chinook. We compare our results to both spawning data from the field and output from other habitat suitability models. Our results, in conjunction with other datasets (e.g. threats, current fish use), can inform decisions on which locales to prioritize for restoration and protection activities and can be used by biologists and managers to estimate the relative size of historical populations.