Stochastic demographic analysis of the pelagic thresher shark (Alopias pelagicus) in the Ecuadorian Pacific

Abstract

The pelagic thresher shark (Alopias pelagicus) is one of the most frequently landed species in Ecuador. However, its population has not been thoroughly assessed due to the lack of historical catch and fishing effort data, which precludes the use of classical stock assessment models. Consequently, this study aimed to evaluate the status of A. pelagicus in Ecuador using models designed for data-poor situations, which rely solely on life history parameters. Specifically, an age-structured model based on Leslie's matrix was used. Due to the uncertainty surrounding life history parameters, stochasticity was incorporated using various types of statistical distributions through Monte Carlo simulations. The results indicate that, in the absence of fishing, the population grows at approximately 8 % per year. However, under current fishing levels, the population is declining at a rate of about 5 % annually. Additionally, there is an 85.71 % excess in current fishing levels required to maintain a stable population. These results probably suggest that this stock is overexploited in the Ecuadorian Pacific. Different management scenarios suggest that juveniles are the most sensitive to fishing mortality. Therefore, urgent, and strict management measures are required in Ecuador to protect juveniles, such as implementing a minimum capture size above the L₅₀ (151.4 cm of precaudal length) and protecting pregnant females.