Miller, Jessica A. 1993. Juvenile chinook (Oncorhynchus tshawytscha) and coho (O kisutch) salmon in natural and created estuarine habitats: Foraging and daily growth. M.S.
Juvenile salmon foraging, growth, and residence patterns were compared in a created and an adjacent natural estuarine slough on the Chehalis River in Washington to address the question of whether artificially constructed habitats provide rearing area similar to natural habitats. Diet analyses, mark-recapture data, and otolith microstructure analyses of sub-yearling chinook, Oncorhynchus tshawytscha, and coho, O. kisutch, salmon residing in both sloughs during spring 1991 and 1992 provided a framework to assess the efficacy of the created habitat in providing rearing habitat. Juvenile chinook and coho diets were mainly aquatic and terrestrial insects in both the created and natural slough. The order of importance of these main prey items differed between sloughs. Stomach fullness indices were significantly lower in the created slough than the natural slough in both 1991 and 1992. Juvenile salmon predators, northern squawfish, Ptychocheilus oregonensis, and yearling coho were consistently found in higher densities in the created than the natural habitat. The greater depth and width of the created slough appeared to favor the presence of fish predators and reduce available refuge sites and decrease foraging efficiencies of juvenile salmon. No significant differences in the pattern and width of daily otolith growth increments of sub-yearling coho were seen between the natural and created sloughs. Otolith microstructure analysis may not be sensitive enough to detect short-term differences in growth. The combined analyses indicate the created estuarine slough in the lower reaches of the Chehalis River is providing rearing habitat for migrating juvenile salmon nearly comparable to the adjacent natural slough. Presently, this study is one of the first to directly evaluate fish use of a compensatory mitigation site in relation to a natural reference site.