Spatial and temporal segregation of wild and hatchery winter steelhead populations in Eagle Creek, Oregon

Abstract

A segregated hatchery program promotes conservation by limiting the amount of overlap in return timing and spawning locations of hatchery- and natural-origin fish. The objective of the present study was to use radiotelemetry data collected from 2005 to 2007 to better understand the level of spatial and temporal segregation between hatchery and natural-origin steelhead Oncorhynchus mykiss in the Eagle Creek basin, Oregon. The analysis resulted in three key findings. First, hatchery-origin winter steelhead were unlikely to migrate into the North Fork Eagle Creek, a tributary that has historically lacked any hatchery releases or influence, suggesting a high level of segregation from the natural-origin population returning to that stream. Second, hatchery fish arrived at the lower fish ladder on Eagle Creek and at Eagle Creek National Fish Hatchery (NFH) earlier than natural-origin fish, suggesting that broodstock management practices to maintain an early returning hatchery stock (i.e., temporal segregation) have been somewhat successful. Finally, regardless of the differential arrival timing to Eagle Creek NFH, there is evidence of an increased probability of spatial and temporal overlap of the populations as the return progresses, and this may be explained by successful reproduction of hatchery-origin fish in main-stem Eagle Creek. Integrated and segregated hatchery programs should be monitored periodically to ensure that they are meeting their stated goals.