Population responses of Coho and Chinook salmon to sedimentation associated with forest roads in a coastal watershed of the lower Fraser River

In British Columbia, one of the main negative impacts on salmonid habitat is the production of fine sediments generated by forest roads or other human activities. Given this concern, this study’s main objective was to develop a quantitative framework for estimating effects of extreme suspended-sediment events caused by forest road construction and use on populations of chinook (Oncorhynchus tshawytscha) and coho salmon (Oncorhynchus kisutch) in a medium-sized coastal watershed of the lower Fraser River. The framework incorporates existing knowledge of sediment production by forest roads to make a quantitative link between traffic levels and physiological responses of salmonids. The results suggest that extreme sedimentation events generated by heavy traffic levels negatively affect populations of chinook and coho. Population numbers declined proportionally to the elevated levels of suspended sediments concentrations following a non-linear trend in which Chinook salmon are more vulnerable to the deleterious effects of sediments than coho salmon.