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Abstract Translocation of adult salmon is an expanding management tactic, especially in rivers with impassable dams. Understanding the productivity of translocated adults compared to donor populations and contribution to subsequent adult returns (i.e., via cohort replacement rate CRR) is critical to evaluating the efficacy of translocation programs. However, empirical CRR estimates are difficult to generate due to life history (LH) complexity, including spatiotemporal diversity created by translocation protocols and diverse juvenile rearing habitats. We built a CRR model for spring-run Chinook Salmon Oncorhynchus tshawytscha in Oregon’s North Santiam River, where two large dams lack fish passage facilities. The model estimates relative replacement metrics for two adult groups: below-dam spawners and above-dam spawners translocated into historical upstream habitat. It also tracks the relative contributions of 13 distinct juvenile phenotypes (i.e., “LH pathways”): 3 produced by the below-dams group and 10 from the above-dams group that includes reservoir-rearing pathways. The fractional CRR of LH pathways varied by 60-fold, with higher CRR for less common spring yearling smolt LHs. Simulated management scenarios indicated low likelihood of replacement of the original adult cohort. The approach provides a framework for evaluating trade-offs and feedbacks among intraspecific diversity, management actions, and LH pathway composition in spatially structured migratory populations.
Keefer et al. (Mon,) studied this question.