Life Cycle Modeling to Quantify Population Level Effects of Reintroduction

The population level effects of reintroduction are uncertain.  In many cases, the region to which anadromous salmonids are being reintroduced has been altered, and the historical accounts of salmon utilizing the region may not have been quantified.  Still, there is a growing body of knowledge regarding the population dynamics of salmonids that can be used to understand the potential change in population abundance due to reintroducing anadromous salmonids to previously utilized habitat.  In the Klamath River, Oregon Chinook salmon (Oncorhynchus tshawytscha) were historically present in the tributaries to Upper Klamath Lake.  A plan to reintroduce fall-run Chinook concurrent with removal of four mainstem dams (Iron Gate, Copco I, Copco II, and J.C. Boyle) is being evaluated.  A single-stock production model was used to evaluate the hypothetical removal of the dams in 2020 and the implementation of programs described in the Klamath Basin Restoration Agreement.  The model consists of two stages: 1) spawners to age 3 in the ocean and 2) age 3 in the ocean to spawners.  The first stage was modeled as a Ricker stock production function based on Klamath River fall run Chinook natural escapement estimates and cohort reconstruction data.  Annual variability in survival to age 3 was modeled as a function of ocean conditions and Klamath River conditions during outmigration.  The coefficients for the first stage model were estimated via a Bayesian analysis of spawner to age 3 abundances for brood years 1979 to 2000.  The second life stage was modeled using the Klamath Harvest Rate Model (KHRM) which was developed by NMFS Southwest Fisheries Science Center to mimic the harvest management of the Klamath River fall Chinook fishery.   The KHRM begins with age 3 fish in the ocean and determines their overall fate (harvest, maturation and escapement, residence in the ocean to age 4, or natural mortality).  In a similar fashion, the KHRM determines the fate of 4 year olds and 5 year olds.  The increase in additional spawning habitat was modeled as a function of watershed area through relationships developed in Liermann et al. (2010) for ocean type Chinook.  The model quantifies the increases in harvest, predictability of harvest (standard deviation of harvest), and stability of fishery (proportion of fishery closures) using Monte Carlo simulation.  To understand the effects of reintroduction, I compared these metrics relative to a baseline scenario without dam removal and without reintroduction.