Release strategies affect the freshwater residence and survival of hatchery-reared juvenile Chinook Salmon
ObjectiveThis study investigated the effects of size, location and timing of release on the freshwater residence and survival hatchery-reared Chinook Salmon (Oncorhynchus tshawytscha) in the Toquaht River, BC. MethodsJuvenile salmon were PIT tagged and released on three separate dates (May 23, June 9 and 19, 2021) and three distinct locations within the river (lower river [below lake], lake, and upper river [above lake]). Fish were detected near the river mouth using a PIT array, and detection data were analyzed with an integrated model of freshwater residence and capture-recapture using Bayesian inference. ResultThe median duration of freshwater residence was 13.8 days and was longer for fish released in the lake and upper river earlier in the study. The median survival probability was 0.35 and it was higher for fish released in the lake and upper river later in the study. Both freshwater residence time and survival declined with fish size at release. ConclusionThese findings highlight that hatchery release strategies can significantly influence survival and freshwater residence times, underscoring the need for adaptable management practices. Impact statementJuvenile Chinook Salmon survival during freshwater residence and outmigration is strongly influenced by hatchery release strategies, thus optimizing these strategies is key for hatcheries to support the recovery of salmon populations.