Forecast Modeling for Oregon Coast Coho: The Benefit of Using Available Life Stage Specific Data

Accurate forecast of adult abundance allows fishery managers to allocate harvest rates that maintain sufficient escapement to support recovery and ecological and cultural objectives for coho salmon populations in the Oregon Coast ESU. Forecast models predict productivity using multiple marine components with spawner abundance as the only freshwater indicator, disregarding the survival of juvenile coho in over 8,000 km of streams for half of the life cycle. The currently accepted forecast model incorporates parental abundance and a suite of oceanographic indicators using generalized additive models to predict the number of adults in the ocean (recruits). The recently accepted harvest matrix adds an early marine survival component based on the return of two-year-old jack salmon. While these models provide some understanding of overall productivity, model components are almost entirely marine based. We propose to incorporate coho summer parr abundance and an overwinter survival rate which can substantially increase the accuracy of the forecast. Deconstructing the variability in life stage specific survival rates can inform recovery monitoring and provide the opportunity to better understand factors related to abundance, distribution, and survival from spawner to adult recruit.