Evaluation of Fall Chinook and Chum Salmon Spawning Habitat near Ives and Pierce Islands in the Columbia River, Progress Report 1999-2001

摘要

The area around Ives Island below Bonneville Dam on the Columbia River supports spawning populations of chum and fall chinook salmon. Because this area is sensitive to water level fluctuations caused by changes in discharge from Bonneville Dam and from tidal cycles, we initiated a study to quantify flow-dependent changes in available spawning habitat for chum and fall chinook salmon. We conducted surveys to characterize the substrates available in the Ives Island study area. Detailed bathymetry was also obtained to serve as a foundation for two-dimension hydrodynamic modeling, which was used to estimate water velocities, depths, and wetted area over a range of simulated flows. Habitat surveys were conducted and logistic regression was used to identify physical habitat variables that were important in determining the presence of chum and fall chinook salmon redds. The physical habitat data were analyzed using the logistic regression models to create probability coverages for the presence of redds in a Geographic Information System. There was generally good agreement between chum and fall chinook salmon redd locations and areas where we predicted suitable spawning habitat. We found that at Columbia River discharges less than 120 kcfs, an important chum salmon spawning area below the mouth of Hamilton Creek could only be supported by discharge from Hamilton Creek. Chum salmon did not appear to spawn in proportion to habitat availability, however our predictive model did not include all variables known to be important to chum salmon redd-site selection. Fall chinook salmon spawning habitat was less sensitive to flow and the main channel of the Columbia River along Pierce Island was predicted to contain sufficient habitat at all modeled flows.