The rapid expansion of human activities threatens ocean-wide biodiversity. Numerous marine animal populations have declined, yet it remains unclear whether these trends are symptomatic of a chronic accumulation of global marine extinction risk. We present the first systematic analysis of threat for a globally distributed lineage of 1,041 chondrichthyan fishes—sharks, rays, and chimaeras. We estimate that one-quarter are threatened according to IUCN Red List criteria due to overfishing (targeted and incidental). Large-bodied, shallow-water species are at greatest risk and five out of the seven most threatened families are rays. Overall chondrichthyan extinction risk is substantially higher than for most other vertebrates, and only one-third of species are considered safe. Population depletion has occurred throughout the world’s ice-free waters, but is particularly prevalent in the Indo-Pacific Biodiversity Triangle and Mediterranean Sea. Improved management of fisheries and trade is urgently needed to avoid extinctions and promote population recovery.DOI: http://dx.doi.org/10.7554/eLife.00590.001

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ABSTRACT1. Fishing spans all oceans and the impact on ocean predators such as sharks and rays is largely unknown. A lack of data and complicated jurisdictional issues present particular challenges for assessing and conserving high seas biodiversity. It is clear, however, that pelagic sharks and rays of the open ocean are subject to high and often unrestricted levels of mortality from bycatch and targeted fisheries for their meat and valuable fins.2. These species exhibit a wide range of life-history characteristics, but many have relatively low productivity and consequently relatively high intrinsic vulnerability to over-exploitation. The IUCN } World Conservation Union Red List criteria were used to assess the global status of 21 oceanic pelagic shark and ray species.3. Three-quarters (16) of these species are classified as Threatened or Near Threatened. Eleven species are globally threatened with higher risk of extinction: the giant devilray is Endangered, ten sharks are Vulnerable and a further five species are Near Threatened. Threat status depends on the interaction between the demographic resilience of the species and intensity of fisheries exploitation.4. Most threatened species, like the shortfin mako shark, have low population increase rates and suffer high fishing mortality throughout their range. Species with a lower risk of extinction have either fast, resilient life histories (e.g. pelagic stingray) or are species with slow, less resilient life histories but subject to fisheries management (e.g. salmon shark).5. Recommendations, including implementing and enforcing finning bans and catch limits, are made to guide effective conservation and management of these sharks and rays.

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Effective ocean management and conservation of highly migratory species depends onresolving overlap between animal movements and distributions, and fishing effort.However, this information is lacking at a global scale. Here we show, using a big-data approach that combines satellite-tracked movements of pelagic sharks and global fishing fleets, that 24% of the mean monthly space used by sharks falls under the footprint of pelagic longline fisheries. Space-use hotspots of commercially valuable sharks and of internationally protected species had the highest overlap with longlines (up to 76% and 64%, respectively), and were also associated with significant increases in fishing effort.We conclude that pelagic sharks have limited spatial refuge from current levels of fishing effort in marine areas beyond national jurisdictions (the high seas). Our results demonstrate an urgent need for conservation and management measures at high-seas hotspots of shark space use, and highlight the potential of simultaneous satellite surveillance of megafauna and fishers as a tool for near-real-time, dynamic management.Industrialised fishing is a major source of mortality for large marine animals (marine megafauna) 1-6 . Humans have hunted megafauna in the open ocean for at least 42,000 years 7 , but international fishing fleets targeting large, epipelagic fishes did not spread into the high seas (areas beyond national jurisdiction) until the 1950s 8 . Prior to this, the high seas constituted a spatial refuge largely free from exploitation as fishing pressure was concentrated on continental shelves 3,8 . Pelagic sharks are among the widest ranging vertebrates, with some species exhibiting annual ocean-basin-scale migrations 9 , long term trans-ocean movements 10 , and/or fine-scale site fidelity to preferred shelf and open ocean areas 5,9,11 . These behaviours could cause extensive spatial overlap with different fisheries from coastal areas to the deep ocean. On average, large pelagic sharks account for 52% of all identified shark catch worldwide in target fisheries or as bycatch 12 . Regional declines in abundance of pelagic sharks have been reported 13,14 , but it is unclear whether exposure to high fishing effort extends across ocean-wide population ranges and overlaps areas in the high seas where sharks are most abundant 5,13 .Conservation of pelagic sharkswhich currently have limited high seas management 12,15,16would benefit greatly from a clearer understanding of the spatial relationships between sharks' habitats and active fishing zones. However, obtaining unbiased estimates of shark and fisher distributions is complicated by the fact that most data on pelagic sharks come from catch records and other fishery-dependent sources 4,15,16 .Here, we provide the first global estimate of the extent of space use overlap of sharks with industrial fisheries. This is based on the analysis of the movements of pelagic sharks tagged with satellite transmitters in the Atlantic, Indian and Pacific oceans, together with fishing vessel movements m...

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Distribution, reproduction and feeding of the Greenland shark Somniosus (Somniosus) microcephalus, with notes on two other sleeper sharks, Somniosus (Somniosus) pacificus and Somniosus (Somniosus) antarcticusThe size and depth distribution, stomach contents and reproductive status of Somniosus (Somniosus) microcephalus, Somniosus (Somniosus) pacificus and Somniosus (Somniosus) antarcticus were examined from specimens collected from the North and South Atlantic, North and South Pacific, and the Southern Ocean. Specimens ranged in size from 42 to 480 cm total length, L T , and were taken from depths of 35-1280 m. Stomach contents included coelenterates, gastropods, cephalopods, echinoderms, crustaceans, elasmobranchs, teleosts, penguins, marine mammals and human waste. Female S. (S.) microcephalus mature at c. 450 cm and S. (S.) antarcticus at c. 435 cm L T ; a female S. (S.) pacificus of 430 cm was mature. Male S. (S.) microcephalus mature at c. 300 cm, but male S. (S.) antarcticus may not mature until c. 400 cm L T . The size at birth in these three species of Somniosus is c. 40 cm L T . # 2007 CSIRO Marine and Atmospheric Research # 2007 CSIRO Marine and Atmospheric ResearchThe three species in the subgenus Somniosus can attain a total length (L T ) of 5-7 m (Compagno, 1984;Cherel & Duhamel, 2004;Compagno et al., 2005). Due to their large size, deep-sea habitat and lack of commercial importance, their biology is poorly known (Castro, 1983;Compagno, 1984;Ebert et al., 1987). This study collected new information on the depth and size distribution, stomach contents and reproductive status of Somniosus (Somniosus) microcephalus, S. (S.) pacificus and S. (S.) antarcticus. MATERIALS AND METHODSA total of 49 S. (S.) microcephalus (64Á8-480Á0 cm L T ) were examined. These included 32 females and 13 males from the western coast of Greenland, one male from Iceland, one male from Boston, U.S.A., and two females from the Canary Islands. Of 34 Somniosus (S.) pacificus (41Á8-430Á0 cm L T ) examined, 14 females and six males were from the eastern Aleutian Islands, Bering Sea and Gulf of Alaska, one male and four females from Japan (Suruga Bay, Sagami Bay and Hiraiso, Ibaraki) and eight females and one male from California, U.S.A. A total of 24 Somniosus (S.) antarcticus (100Á0-438Á0 cm L T ) were examined. These included 14 females and five males from the Tasman Sea and Macquarie Island, three females from South Africa and two males from Namibia.Specimens were caught with demersal trawls, longlines, droplines and gillnets; fishing gear is described in Yano (1995), Yano & Dahlheim (1994) and Yano & Tanaka (1984).Ln-converted L T and mass equations for S. (S.) microcephalus, S. (S.) pacificus and S. (S.) antarcticus were calculated by the least squares method. Curves for these three species (by sex) were fitted to the data using the formula:mass in kg, L T is in cm, and a and b are fitted constants. Stomachs from 39 S. (S.) microcephalus collected from western Greenland waters, 21 S. (S.) pacificus from the Bering Sea, Gulf of ...