Preliminary Stock Synthesis (SS3) model runs conducted for north Atlantic blue shark

Preliminary Stock Synthesis model runs were conducted for North Atlantic blue sharks based on the available catch, CPUE, length composition, and life history data compiled by the Shark Working Group. A combined sex model was implemented in order to reduce model complexity. Beverton-Holt stock-recruitment was assumed. The steepness of the stock recruitment relationship and natural mortality at age were fixed at independently estimated values. Several preliminary model runs resulted in unreasonable convergence diagnostics, and model results were sensitive to the sample sizes (weights) assigned in the model likelihood to length composition data. Two preliminary model runs which utilized multiplication factors to reduce the input sample size assigned to length composition data in the model likelihood resulted in reasonable convergence diagnostics. Model fits to CPUE and length composition data were similar for both models. Both models resulted in sustainable spawning stock size and fishing mortality rates relative to maximum sustainable yield. The model with a relatively lower sample size assigned to the length composition data resulted in a relatively more depleted stock size.