Population Responses of Chinook and Coho Salmon to Suspended Sediments in a Coastal Watershed of British Columbia

Increased suspended sediments (SSC) over background levels affect salmonids at all life stages. Although many studies have investigated the individual response of salmonids to suspended sediments, to our knowledge, none has addressed the issue of increased SSC at the population level. Thus, this study’s main purpose was to develop a quantitative framework for estimating the effects of extreme suspended-sediment events on populations of Chinook and coho salmon in a coastal watershed of the Lower Fraser River. To do so, we used a life history model coupled with a set of simulated time series of suspended sediments derived from several of forest road management scenarios. The results suggest that intensive use of forest roads, which generated an increase in the frequency and magnitude of extreme sedimentation events, caused marked reductions on the populations of study. Furthermore, the populations of both Chinook and coho declined exponentially for a linear increase in the number of extreme sedimentation events (SSC > 25 mg/L), although this decline was more evident for Chinook salmon. The model presented here could provide insights into forestry impacts on watershed hydrological processes, and assist resource managers with planning effective conservation strategies of natural resources in multiple-use watersheds.