|Title:||In-water restoration between Miller Sands and Pillar Rock Island, Columbia River: biological surveys, 1992|
|Author/Editor:||George T. McCabe, Robert L. Emmett, Susan A. Hinton|
|Institution:||National Marine Fisheries Service, Northwest Fisheries Science Center. Seattle|
In 1992, we initiated a study of benthic invertebrates, fish, and sediment characteristics at a proposed habitat restoration area vs. an adjacent shallow subtidal habitat area. Both areas were located between Miller Sands and Pillar Rock Island. Primary objectives of the research were to document existing biological communities and provide habitat criteria for disposal of dredged material at the proposed habitat restoration area. Major differences between study areas were identified. Total benthic invertebrate and C. salmonis densities were significantly higher in the shallow subtidal habitat than in the proposed habitat restoration area (P < 0.05). In addition, there were major differences in sediment characteristics between study areas. Median grain size was significantly higher in the proposed habitat restoration area than in the shallow subtidal habitat, whereas percent volatile solids were significantly lower in the proposed habitat restoration area than in the shallow subtidal habitat. Percent silt/clay was also lower in the proposed habitat restoration area (mean 0.2%) than in the shallow subtidal habitat (mean 8.5%). Although densities of juvenile salmonids in the proposed habitat restoration area and shallow subtidal habitat were similar in both months of this study, the shallow subtidal habitat is probably more valuable to salmonids because of the larger standing crops of C. salmonis. Results from 1992 suggest that the habitat value of the proposed restoration area could be enhanced by proper placement and stabilization of dredged material from the Columbia River. However, additional sampling is required to substantiate these results. In addition, hydraulic modeling studies in progress by the COE need to be completed to determine if any adverse changes in water circulation in the Columbia River estuary would result from the proposed habitat modification.