Temporal and Spatial Occurrence of Female Chinook Salmon Carrying a Male-Specific Genetic Marker in the Columbia River Watershed

Recent declines in many chinook salmon, Oncorhynchus tshawytscha, populations within the Columbia River watershed have prompted an examination of their reproductive biology. In a previous study many female fall chinook salmon collected in 1999 from the Hanford Reach of the Columbia River tested positive for a male-specific DNA marker (OtY1) found on the Y chromosome. The purpose of this study was to determine if females testing positive for the OtY1 marker could be found in other populations of fall chinook salmon from the Columbia River, and to assess the prevalence of OtY1 incidence in different female cohorts. Post-spawned male and female fall chinook salmon from three different naturally spawning populations (Hanford Reach, Yakima River and Ives Island) and one hatchery population (Priest Rapids Hatchery) on the Columbia River were tested in 2000 and 2001 for the OtY1 marker. Among naturally spawning populations, 57.4% of the females tested positive from the Hanford Reach, 33.3% tested positive from the Yakima River, and 32.5% tested positive from Ives Island. Of the Priest Rapids Hatchery fish, 62.5% of the females tested positive, and significant differences were detected between the 1995–1996 and 1997–1998 female cohorts from this population. No significant differences were detected between any of the female cohorts from the naturally spawning populations. All male chinook salmon samples, tested positive for OtY1.