Bayesian estimation of the age and growth of the pelagic thresher shark (Alopias pelagicus) from the Mexican Pacific

The pelagic thresher shark (Alopias pelagicus) is considered overexploited; however, information about its biology in the Eastern Pacific is scarce, particularly age estimation and growth modeling. Age was estimated by counting growth bands in the cervical vertebrae. Specimens, ranging in size from 85.00 to 174.90 cm precaudal length (PCL), were collected by pelagic longliners in 2020 and 2021. Three different growth models (von Bertalanffy, Gompertz, and logistic) were applied to the length-at-age data. Bayesian methods using the Markov chain Monte Carlo algorithm were employed for parameter estimation. Based on the Watanabe–Akaike information criterion for model selection, the von Bertalanffy was selected as the best model for both sexes combined, with the estimated parameters being PCL₀ = 86.20 cm (95% credible interval (CI_95%), 83.03‒89.32), PCL_∞ = 180.66 cm (CI_95%, 172.96‒189.81), and k = 0.09 year⁻¹ (CI_95%, 0.07–0.10). These results suggest that females and males have the same growth pattern. Based on known size at maturity, age at maturity for the pelagic thresher shark was estimated at 7 years for males and 9 for females, with a maximum lifespan of 22 to 38 years. This study provides crucial life history information that can contribute to managing and conserving this endangered species.