Effects of Invasive Reed Canarygrass (Phalaris arundinacea) on Rearing Habitat and Feeding of Juvenile Chinook Salmon (Oncorhynchus tshawytscha) in the Upper Columbia River Estuary

Thirteen native Columbia River salmon stocks are listed under the Endangered Species Act, impacting one of the Pacific Northwest’s most important recreational, commercial, and subsistence fisheries. Juvenile Chinook salmon utilize wetland channels for rearing habitat; therefore, many resource managers in Oregon and Washington are working to restore tidal wetland habitats. Reed canarygrass (RCG) is a highly invasive aquatic plant species that affects a number of wetlands in the upper Columbia River estuary, including the site of this study, Multnomah Channel Marsh. The presence of RCG undoubtedly reduces plant diversity, but how it impacts native fishes is unclear. Hatchery-raised juvenile Chinook salmon, placed in pens on floodplain microhabitats dominated by RCG and by native vegetation (i.e. Carex aperta), allow for comparisons of growth, feeding, and prey sources (stomach content and invertebrate analysis) in the two habitats. The study further identifies disparities in feeding characteristics for juvenile salmonids collected in Multnomah Channel and the Columbia mainstem, to evaluate differences in diet along a habitat gradient. This study seeks to elucidate the role of RCG and its effects (direct and indirect) on salmonid rearing habitat and diet, and provide information on the tradeoffs associated with RCG control measures for salmon.