Differential Timing and Distribution of Natural-Origin and Hatchery Sockeye Salmon Spawning Naturally in the Cedar River, WA

Sockeye salmon (Oncorhynchus nerka) carcasses were recovered from the spawning grounds to assess characteristics of the natural spawning population and provide data to support management of the Cedar River Hatchery. Sagittal otoliths were analyzed to separate wild and hatchery reared sockeye by identification of unique marks created by thermal chilling of embryos prior to release (n=790). We compared the proportion of wild and hatchery origin sockeye in the spawning population and investigated differences in the temporal and spatial distribution of spawning. The proportion of hatchery origin sockeye in the Cedar River (PHOR=0.35) was similar to the proportion taken for broodstock (PHOR=0.45). Hatchery origin sockeye spawned earlier than wild sockeye. The release site of hatchery reared fry significantly influenced the distribution of their carcass recovery locations. Sockeye fry released near the mouth of the Cedar River were more likely to be recovered as adults in the lower reaches while individuals released as fry at river mile 13.5 were more likely to be recovered higher in the river. These results suggest that release site of sockeye fry from the Cedar River Hatchery can influence the location where adults spawn upon their return to the river and provides support for informed management decisions.