A Fish Out of Basin: Increased Stress Physiology and Reduced Performance of Salmon River Hatchery Chinook Salmon

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AbstractVariation in rearing conditions across hatcheries and basins can affect the performance of hatchery salmonids in the wild. In 2008, the Shoshone‐Bannock Tribes began planning an out‐of‐basin hatchery facility on the eastern Snake River Plain for rearing threatened Chinook Salmon Oncorhynchus tshawytscha for release in tributaries of the upper Salmon River, Idaho, USA. To help determine the viability of the planned out‐of‐basin hatchery, we reared 100,000 juvenile Chinook Salmon from the same genetic stock at one in‐basin (Sawtooth Fish Hatchery on the Salmon River) and one out‐of‐basin (Springfield Fish Hatchery on the Snake River Plain) site in Idaho that are characterized by significant differences in water hardness and temperature regime. In October 2018 and April 2019, we tested whether fish condition, stress physiology, acute mortality, and downstream survival differed between the two groups at the parr and smolt life stages upon release in the Yankee Fork Salmon River, which is characterized by low water hardness. For both release groups, parr experienced low acute mortality during the 48 h after release; however, the out‐of‐basin group had a downstream survival rate through an unimpounded portion of the migration corridor that was an order of magnitude lower than that for the in‐basin group. During the smolt release, the out‐of‐basin group showed signs of extreme physiological stress, acute mortality rates of 40–80%, and low survival in the unimpounded portion of the migratory corridor. The in‐basin group recovered from the stress of transport and release, had no acute mortality, and survived through the unimpounded migratory corridor at a rate comparable to that of previous years’ releases. Based on the results of this comparative study, comanagers are evaluating alternatives to the proposed out‐of‐basin hatchery program. This case study highlights the effects of differences between rearing and release conditions on salmon physiology and survival as well as the value of conducting preliminary evaluations prior to implementing large‐scale hatchery supplementation programs.