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Overexploitation threatens the future of many large vertebrates. In the ocean, tunas and sea turtles are current conservation concerns because of this intense pressure. The status of most shark species, in contrast, remains uncertain. Using the largest data set in the Northwest Atlantic, we show rapid large declines in large coastal and oceanic shark populations. Scalloped hammerhead, white, and thresher sharks are each estimated to have declined by over 75% in the past 15 years. Closed-area models highlight priority areas for shark conservation, and the need to consider effort reallocation and site selection if marine reserves are to benefit multiple threatened species.
Human exploitation has propagated across land, coastal areas, and the ocean, transforming ecosystems through the elimination of many species, particularly large vertebrates (1, 2). Only in the past half century, as fishing fleets expanded rapidly in the open ocean, have large marine predators been subject to this intense exploitation. Many species, including tuna, billfishes (3), and sea turtles (4), are of immediate conservation concern as a result. Among the species impacted by these fisheries, sharks should be of particular concern. Despite their known vulnerability to overfishing (5, 6), sharks have been increasingly exploited in recent decades, both as bycatch in pelagic longline fisheries from the 1960s onward (7) and as targets in directed fisheries that expanded rapidly in the 1980s (8). The vast geographic scale of pelagic marine ecosystems constrains our ability to monitor shark populations adequately. Thus, the effect of exploitation on sharks has, for most populations, remained unknown (9). Shark management and conservation have been hindered by the lack of knowledge on their status or even the direction of the population trends.
We present an analysis of logbook data for the U.S. pelagic longline fleets targeting swordfish and tunas in the Northwest Atlantic (Fig. 1). Pelagic longlines are the most widespread fishing gear used in the open ocean. The data set presented is the largest available for this region (214,234 sets between 1986 and 2000 with a mean of 550 hooks per longline set) and includes one of the longest time series for sharks. Six species or species groups were recorded from 1986 onward, and eight species from 1992 onward (Table 1). For most shark species examined, this is the...