Abundance Trends of Highly Migratory Species in the Atlantic Ocean

Abundance trends of highly migratory species (HMS) have played a central role in debates over the health of global fisheries. However, such trends have mostly been inferred from fishery catch rates, which can provide misleading signals of abundance. While many biases are accounted for through traditional catch rate standardization, habitats are often not directly considered. Using a method that explicitly accounts for temperature in areas fished, we estimated abundance trends for 35 HMS in the Atlantic Ocean from 1987 through 2010. This represents one of the largest studies of HMS population trends. Overall, a majority of HMS (74% of analyzed species) are either declining in abundance or declined initially with no evidence of rebuilding. Conversely, 26% of the species exhibited stable, increasing, or recovering trends; however, these trends were more prevalent among tunas than either billfish or sharks. By including temperature in our analyses, we observed the effects of physical habitat on fishery catch rates; thus, our results can help guide management regulations aimed at reducing incidental catch of certain species by avoiding the habitats in which catch rates of incidental species were highest.