Estimating age-at-maturity for individual Atlantic bluefin tuna (Thunnus thynnus) from back-calculated growth trajectories

We fit a biphasic Lester Model to back-calculated size-at-age data for Atlantic bluefin tuna (Thunnus thynnus) captured in the western Atlantic management area that had been genetically assigned to either the western (Gulf of Mexico) or eastern (Mediterranean) spawning stocks. We tested the hypothesis that spawning-stock variation exists in age-at-maturity for this species using a Bayesian approach to incorporate and compare the support for different growth models and maturity scenarios considered for the western spawning stock. The biphasic Lester Model out-performed the uniphasic von Bertalanffy model and showed good fits for describing individual growth variability in Atlantic bluefin tuna. The Lester Model provided estimates of individual age-at-maturity and spawning, from which spawning ogives were generated and compared to two reproductive scenarios currently considered for the western spawning stock; either an early (age at 50 % maturity at 4 years) or late maturity scenario (age at 50 % maturity at 10). The results derived from the Lester Model demonstrate a lack of stock-specific variation in reproductive dynamics for Atlantic bluefin tuna, and provide support for an early maturity scenario for the western spawning stock.