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Upper Yakima River Steelhead demographics

Notes:

Upper Yakima steelhead demographics. Age structures from scale sampling 100% of returning adults at the Roza facility between 2002-2005 showed that upper yakima river steelhead spend 1 to 2 years in the ocean before returning to freshwater and a small percentage are repeat offenders, spawners. Freshwater age composition range from 1 to 4 years of age at smoltification with a dominant age class of 2 year olds. Sex ratios, highly skewed toward females with nearly 80%. A potential source or causal mechanism of this phenomena could be related to the male progeny derived from anadromous females are actually contributing to the resident population, thus, skewing the sex ratios of the returning adult anadromous life history form.