Hatchery production has supplemented the Sacramento River winter-run Chinook salmon population since they first became listed in 1989. While the primary purpose for producing juveniles is to increase abundance, hatchery-produced individuals are also a valuable tool in monitoring the endangered population. Hatchery fish can be tagged prior to their release to provide insight into river and ocean conditions their wild counterparts may be experiencing. Hatchery fish often serve as surrogates for wild fish to estimate vital rates, movement and fishery contact rates. Due to differences in rearing conditions and release timing, hatchery-origin fish may behave differently and have life histories that differ from natural-origin fish, resulting in inaccuracies when deriving vital rates for the total population.
The researchers of this project evaluated when it is appropriate to apply estimates derived from hatchery-origin individuals in management tools for the whole population. Researchers compared the migration behavior and age structure of hatchery- and natural-origin fish using otoliths and scales, which can be examined to understand their habitat use and life history. Preliminary results comparing hatchery- and natural-origin life history suggest hatchery fish have more homogenous outmigration and maturation behavior.
Values derived from winter-run hatchery fish are used to inform water project operations in the Central Valley, set allowable catches for the ocean fishery and prioritize conservation goals in California. Evaluating an assumption commonly made is imperative to understanding potential biases that influence these decisions. The results of this research will be used to strengthen the accuracy of existing management tools and the viability of hatchery operations.