How Much Influence Can the Selection of Statistic Estimator Have on Fisheries Stock Assessment: A Case Study in Hammerhead Shark Stock Assessment

    Many shark populations have significantly declined globally in the last few decades. Reasons that led to this alarming situation have been considered to be the slow intrinsic rates of increases of the shark populations and overexploitation from the directed-shark fishery and bycatch. Studies that can help to understand the fishery status and the influence of the fisheries on the shark populations have been critically needed in managing these shark populations. This study is based on the scalloped hammerhead shark Sphyrna lewini, a species globally exploited, which is classified as “Endangered” by the IUCN.

     Past research reports on scalloped hammerhead sharks in the western North Atlantic Ocean have concluded that the population has decreased. However, different statistical tools have provided diverse results on the degree of the decline. In this study, we compare surplus production models with different consideration of errors and estimators. We apply three types of estimators (frequentist, likelihood, and Bayesian) and take into account two kinds of errors (measurement error and process-measurement error) to assess the state of this scalloped hammerhead shark population. The recommendation on the estimator selection will provide better understanding of the population status and help to improve the management of this population.