Broad-Scale Patterns of Abundance in Northwest Atlantic Sharks

A typical shark stock assessment incorporates several spatially limited indices of abundance in order to span the extensive range of the species of interest. Despite measuring the same resource, these indices typically display antagonistic trends that cannot be reconciled by current stock assessment models, hindering our ability to discern population trends. In this study, we analyzed catch data from several fishery-independent surveys along the US east coast and throughout the Gulf of Mexico to create standardized catch-based indices of abundance for select species, including vulnerable large coastal sharks and comparatively productive small coastal species. To combine the indices of abundance in a comprehensive way, we propose utilization of dynamic factor analysis (DFA). Use of DFA allows us to recognize and describe common trends, while extracting drivers of abundance from a collection of time series. We will present results of our collaborative approach applied on northwest Atlantic shark stocks. By estimating the stock-wide abundance as a single index, we can remove the problematic practice of utilizing opposing indices. The outcomes of this research will enhance our understanding of broad-scale shark abundance trends, which is crucial for appropriate management of these inherently susceptible species.