This project extends and advances existing ocean distribution and size models for Chinook Salmon, a major prey of Southern Resident Killer Whales (SRKW) and target of important fisheries, to provide ocean distribution estimates for multiple run-types (fall, summer, and spring Chinook) arising from rivers from California to Alaska by season and under variable oceanic conditions. It leverages very large tag-recapture databases that have been developed for Chinook Salmon over the past 50 years – hundreds of millions of fish tagged and millions recovered – and links these recoveries to a range of fisheries in which Chinook are targeted or captured as bycatch. It integrates data coast-wide, from Alaska to California, and over more than 30 years (1978-2015), to provide a first synthetic, quantitative description of Chinook distribution that can be used to understand the total Chinook prey field available to SRKW, fishers, and other predators in different seasons and under alternate ocean states. In addition, this projects examines long-term trends in Chinook salmon size and their biological implications. Chinook populations have shown pronounced trends toward smaller and younger fish returning to spawn, and these trends have accelerated in the last 15 years. This erosion of the age-size structure and life-history diversity may negatively affect population productivity via reductions in reproductive potential, and may compromise the long-term viability of populations and jeopardize the sustainability of Chinook salmon fisheries. Consequently, long-term shifts in life-history characteristics, which are likely caused by changing ecological conditions in the ocean, might need to be accounted for when estimating reference points for fishery management. This work supports ongoing efforts to recover SRKW populations, informs the SRKW critical habitat designation process and recovery plans, feeds into the PFMC SRKW ad hoc work group, and is directly in line with the NMFS Ecosystem-Based Fisheries Management Road Map and Policy as well as the National Climate Science Strategy.