Population Goals for Reintroduction of Chinook Salmon into the San Joaquin River, California

The primary restoration goal of the San Joaquin River Restoration Program (Program) is spring-run and fall-run Chinook salmon (Oncorhynchus tshawytscha) reintroduction to the San Joaquin River.  The Technical Advisory Committee (TAC) for the Program evaluated the restored river’s potential to support robust salmon populations by considering the following information: (1) historic population estimates; (2) run sizes immediately after Friant Dam was completed; (3) post-dam runs of fall-run Chinook salmon on the Merced, Tuolumne, and Stanislaus rivers below the lowest major dams; (4) estimates of the number of spring-run Chinook salmon spawners and juveniles that can be supported by existing and/or improved habitat (habitat carrying capacity); and (5) basic genetic and demographic models for minimum viable population sizes.  In order to meet the ultimate date by which a self-sustaining population should be established in December 31, 2024, the TAC recommended the implementation of phased population targets as follows: (1) Reintroduction Period [2012 to 2019] = 500 returning spawners; (2) Interim Period [2020 to 2024] = 500 returning spawners (minimum) and five-year running average escapement target of 2,500 fish; (3) Growth Population Period [2025 to 2040] = five-year running average of spawners increase to 30,000 (10,000 for fall-run) and cohort replacement rate >1; (3) Long-term Period [2041+] = five-year running average of 30,000 (10,000 for fall-run) providing for 50% range of fluctuation.  The targets reflect the minimum viable population size (demographic), the minimum effective population size (genetic), and numbers that the habitat can support (carrying capacity). The Program’s Fisheries Management Workgroup developed additional objectives necessary to achieve the population targets in the Fisheries Management Plan: A framework for Adaptive Management in the San Joaquin River Restoration Program. These additional objectives include: (1) prespawn mortality of adult Chinook salmon <15%; (2) mean egg production of female spring-run = 4,200 and egg survival > 50 percent; (3) spring-run juveniles = 44,000 minimum and 1,575,000 maximum, fall-run juveniles = 63,000 minimum and 750,000 maximum; (4) < 10% virulent disease in juvenile salmon; (5) minimum juvenile salmon growth rate in spring = 0.4 grams per day (g/d) and summer = 0.07 g/d; and (6) 10 years following reintroduction salmon of hatchery origin < 15%.  Habitat goals were also established to support the population targets.  The carrying capacity of the existing habitat in the restoration area, and the timing of and fish response to habitat improvements due to restoration actions is uncertain.