Fishing for oil and meat drives irreversible defaunation of deepwater sharks and rays.

The deep ocean is the last natural biodiversity refuge from the reach of human activities. Deepwater sharks and rays are among the most sensitive marine vertebrates to overexploitation. One-third of threatened deepwater sharks are targeted, and half the species targeted for the international liver-oil trade are threatened with extinction. Steep population declines cannot be easily reversed owing to long generation lengths, low recovery potentials, and the near absence of management. Depth and spatial limits to fishing activity could improve conservation when implemented alongside catch regulations, bycatch mitigation, and international trade regulation. Deepwater sharks and rays require immediate trade and fishing regulations to prevent irreversible defaunation and promote recovery of this threatened megafauna group.

Challenges and Priorities in Shark and Ray Conservation.

Sharks, rays, and chimaeras (Class Chondrichthyes; herein 'sharks') are the earliest extant jawed vertebrates and exhibit some of the greatest functional diversity of all vertebrates. Ecologically, they influence energy transfer vertically through trophic levels and sometimes trophic cascades via direct consumption and predation risk. Through movements and migrations, they connect horizontally and temporally across habitats and ecosystems, integrating energy flows at large spatial scales and across time. This connectivity flows from ontogenetic growth in size and spatial movements, which in turn underpins their relatively low reproductive rates compared with other exploited ocean fishes. Sharks are also ecologically and demographically diverse and are taken in a wide variety of fisheries for multiple products (e.g. meat, fins, teeth, and gills). Consequently, a range of fisheries management measures are generally preferable to 'silver bullet' and 'one size fits all' conservation actions. Some species with extremely low annual reproductive output can easily become endangered and hence require strict protections to minimize mortality. Other, more prolific species can withstand fishing over the long term if catches are subject to effective catch limits throughout the species' range. We identify, based on the IUCN Red List status, 64 endangered species in particular need of new or stricter protections and 514 species in need of improvements to fisheries management. We designate priority countries for such actions, recognizing the widely differing fishing pressures and conservation capacity. We hope that this analysis assists efforts to ensure this group of ecologically important and evolutionarily distinct animals can support both ocean ecosystems and human activities in the future.