Landscape-level constraints on recruitment of chinook salmon (Oncorhynchus tshawytscha) in the Columbia River basin, USA

1. The decline of salmonid populations in the Pacific Northwest has been well-documented. It is unclear, however, which threats to salmonid persistence are the most serious, and how best to prioritize recovery efforts intended to ameliorate these threats. 2. It has been argued previously that one possible cause of salmon endangerment is degradation of spawning grounds. In order to explore this hypothesis, this study examines the relationships between chinook salmon (Oncorhynchus tshawytscha) productivity and landscape-level characteristics of spawning grounds in the interior Columbia River Basin. 3. Population productivity is expressed as the mean and maximum recruitment rates for different stocks, measured from 1980 to 1990; habitat conditions are calculated using sub-watershed scale data on land cover, land use, water quality and watershed hydrology. 4. Significant linear regression results were obtained for three environmental variables: percentage of land classified as urban, proportion of stream length failing to meet water quality standards, and an index of the ability of streams to recover from sediment flow events. A multiple regression with all three variables accounts for over 60% of the variation in mean salmon recruitment. 5. It further appears that these landscape attributes may limit the maximum recruitment rates of salmon, with a magnitude of difference in productivity large enough to be relevant to recovery planners. Additional study will be necessary to identify cause-and-effect linkages between habitat quality and salmon recruitment success, and to determine the ultimate impact of changes in recruitment rates on short- and long-term salmon population trajectories. Copyright (C) 2002 John Wiley Sons, Ltd.