A COMPARATIVE-ASSESSMENT OF A NATURAL AND CREATED ESTUARINE SLOUGH ASREARING HABITAT FOR JUVENILE CHINOOK AND COHO SALMON

Short-term otolith growth rates, residence times, and forage of two sp ecies of juvenile salmon (Oncorhynchus spp.) were compared in a create d and natural estuarine slough on the Chehalis River in Washington to assess the functional equivalency of the created slough in providing s uitable rearing habitat. Otolith microstructure, mark-recapture data, and forage of sub-yearling chinook, O. tshawytscha, and coho, O. kisut ch, residing in both sloughs during the spring of 1991 and 1992 served as indicators of rearing habitat quality. No significant differences in the number or width of coho daily otolith increments: were detected between the sloughs. Juvenile chinook residence and emigration times were also comparable. Aquatic and terrestrial insects composed the maj ority of all chinook and coho diets; however,the order of importance o f main prey items did differ between sloughs, and salmon in the create d slough had emptier stomachs, possibly because of reduced prey availa bility and/or foraging efficiency.