Winter-Rearing Temperature Affects Growth Profiles, Age of Maturation, and Smolt-to-Adult Returns for Yearling Summer Chinook Salmon in the Upper Columbia River Basin (original) (raw)

In this investigation, we assessed the effects of rearing conditions on survival and demographics for four yearling summer Chinook Salmon Oncorhynchus tshawytscha hatchery programs from the upper Columbia River basin over four release years. Juveniles from each hatchery program were initially reared at Eastbank Hatchery near Wenatchee, Washington (which uses groundwater for fish rearing), and experienced similar rearing temperatures until their first autumn in culture. Fish from two of the programs were subsequently transferred to surface water acclimation sites, where they were reared until release the following spring (surface water winter rearing). Fish from the other two programs were overwintered at the Eastbank Hatchery and then transferred to their acclimation and release sites one to two months prior to spring release (groundwater winter rearing). These two rearing strategies resulted in contrasting temperature profiles experienced by the fish, which in turn affected winter growth, age at maturation, and smolt-to-adult survival (SAS). Overall, the two release groups that were overwintered on colder surface water experienced reduced winter growth, reduced minijack rate, and smaller size at release, but achieved a two-to threefold higher SAS compared to the two release groups overwintered on warmer groundwater at Eastbank Hatchery. In addition, based on migration data compiled from fish tagged with passive integrated transponder tags, smaller juveniles tended to mature at older age-classes than larger smolts. We conclude that rearing of yearling hatchery summer Chinook Salmon under more natural thermal regimes (surface water) may result in the return of larger, older adults that have a higher survival rate compared with fish reared under constant or less natural thermal regimes (ground water). These results highlight the importance of the hatchery-rearing environment in shaping the survival and life history of summer Chinook Salmon juveniles released into the Columbia River basin.