One of the tasks under Project 199102900 is to complete a two-stage state-space life-cycle model for naturally produced Snake River fall Chinook salmon that can be used to evaluate population viability and recovery strategies. A critical element of the state-space model is quantifying the contribution of measurement error (i.e., sampling variation) from process error (i.e., natural variation) in the life-cycle dynamics of fall Chinook salmon.  To facilitate quantifying the contribution of these error sources, input variables required by the state-space model includes estimates of natural escapement over Lower Granite Dam with estimates of measurement error.  Estimates of natural escapement are available, but to date, no valid estimate of uncertainty is available owing to the difficulty of properly accounting for sources of error such as window count sampling rates, adult trapping rates, fallback, and re-ascension. This contract will adapt an existing statistical model developed for adult spring Chinook salmon to estimate sources and magnitudes of error in fall Chinook salmon abundance estimates.