| Global fisheries collapses are commonplace. However, the effects of exploitation on many marine species remain unclear. This is particularly true for species in pelagic marine ecosystems because the vast geographic scale of these ecosystems constrains our ability to monitor them. Among the species exploited in these ecosystems, sharks should be of particular concern. Sharks are more vulnerable to overfishing than most teleost fishes because of their slow growth, late age at maturity, and low fecundity. Despite this known vulnerability, sharks have been increasingly exploited globally in recent decades, both as bycatch in pelagic longline fisheries and as targets in directed fisheries. In many areas, the effects of exploitation on shark populations are unknown.; Here, I examine the effects of exploitation on shark populations in the Northwest Atlantic using the largest fishery dependent dataset in this region. My research includes the application of new methods and six additional analyses to test the robustness of the results. My conclusions are the same irrespective of the model used.; I provide the first robust large-scale estimates of trends in abundance for scalloped hammerhead, white, tiger, common thresher and oceanic whitetip sharks in the Northwest Atlantic. I demonstrate that there have been substantial declines over the last 8–15 years in all shark populations examined. In particular, declines in relative abundance of scalloped hammerhead, white, and common thresher sharks, each estimated to be over 75% in the last 15 years, represent immediate conservation concerns. The estimated declines are in addition to substantial historical reductions that cannot be so well quantified; my results imply that even the remaining shark populations are now threatened by overexploitation. Similar fishing pressure throughout the world's oceans suggests that the trends estimated here may be reflective of a general phenomenon for these species. |
