Multi-Stock Life Cycle Modeling of Salmonids

Salmon populations migrating through major river systems share a portion of their life history with other populations originating from different natal streams. As juveniles and adults, populations are similarly fated when they are in the same place at the same time because they consume common resources and are subject to the same causes of mortality. Quantitative assessments can be designed to attribute temporal variation in survival commonly across populations sharing a common stage of life history. Given the amount of uncertainty in spawner/recruit data, this presents an opportunity to improve the precision of parameter estimates in stock/recruitment analyses by looking for shared patterns among populations. In this analysis,  the life-cycles of multiple populations are modeled simultaneously. Spawning conditions are modeled uniquely for each population, but survival during rearing, out-migration and spawning migration is integrated among populations. For each population a mixture of shared and population specific productivity and capacity parameters are estimated using maximum likelihood model fitting techniques by comparing observed and predicted abundances and survival rates.  Where environmental indices are available, they are used as forcing variables for parameters values. Model fitting results are compared using information theoretic indices.