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Extinction risk and conservation of the world’s sharks and rays

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      Abstract

      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

      eLife digest

      Ocean ecosystems are under pressure from overfishing, climate change, habitat destruction and pollution. These pressures have led to documented declines of some fishes in some places, such as those living in coral reefs and on the high seas. However, it is not clear whether these population declines are isolated one-off examples or, instead, if they are sufficiently widespread to risk the extinction of large numbers of species.

      Most fishes have a skeleton that is made of bone, but sharks and rays have a skeleton that is made of cartilage. A total of 1,041 species has such a skeleton and they are collectively known as the Chondrichthyes. To find out how well these fish are faring, Dulvy et al. worked with more than 300 scientists around the world to assess the conservation status of all 1,041 species.

      Based on this, Dulvy et al. estimate that one in four of these species are threatened with extinction, mainly as a result of overfishing. Moreover, just 389 species (37.4% of the total) are considered to be safe, which is the lowest fraction of safe species among all vertebrate groups studied to date.

      The largest sharks and rays are in the most peril, especially those living in shallow waters that are accessible to fisheries. A particular problem is the ‘fin trade’: the fins of sharks and shark-like rays are a delicacy in some Asian countries, and more than half of the chondrichthyans that enter the fin trade are under threat. Whether targeted or caught by boats fishing for other species, sharks and rays are used to supply a market that is largely unmonitored and unregulated. Habitat degradation and loss also pose considerable threats, particularly for freshwater sharks and rays.

      Dulvy et al. identified three main hotspots where the biodiversity of sharks and rays was particularly seriously threatened—the Indo-Pacific Biodiversity Triangle, Red Sea, and the Mediterranean Sea—and argue that national and international action is needed to protect them from overfishing.

      DOI: http://dx.doi.org/10.7554/eLife.00590.002

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      Most cited references 163

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      Biodiversity hotspots for conservation priorities.

      Conservationists are far from able to assist all species under threat, if only for lack of funding. This places a premium on priorities: how can we support the most species at the least cost? One way is to identify 'biodiversity hotspots' where exceptional concentrations of endemic species are undergoing exceptional loss of habitat. As many as 44% of all species of vascular plants and 35% of all species in four vertebrate groups are confined to 25 hotspots comprising only 1.4% of the land surface of the Earth. This opens the way for a 'silver bullet' strategy on the part of conservation planners, focusing on these hotspots in proportion to their share of the world's species at risk.
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        A general and simple method for obtainingR2from generalized linear mixed-effects models

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          Global biodiversity: indicators of recent declines.

          In 2002, world leaders committed, through the Convention on Biological Diversity, to achieve a significant reduction in the rate of biodiversity loss by 2010. We compiled 31 indicators to report on progress toward this target. Most indicators of the state of biodiversity (covering species' population trends, extinction risk, habitat extent and condition, and community composition) showed declines, with no significant recent reductions in rate, whereas indicators of pressures on biodiversity (including resource consumption, invasive alien species, nitrogen pollution, overexploitation, and climate change impacts) showed increases. Despite some local successes and increasing responses (including extent and biodiversity coverage of protected areas, sustainable forest management, policy responses to invasive alien species, and biodiversity-related aid), the rate of biodiversity loss does not appear to be slowing.
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            Author and article information

            Affiliations
            deptIUCN Species Survival Commission Shark Specialist Group, Department of Biological Sciences , Simon Fraser University , Burnaby, Canada
            deptEarth to Ocean Research Group, Department of Biological Sciences , Simon Fraser University , Burnaby, Canada
            deptIUCN Species Survival Commission Shark Specialist Group , NatureBureau International , Newbury, United Kingdom
            deptVirginia Institute of Marine Science , College of William and Mary , Gloucester Point, United States
            British Antarctic Survey, Natural Environment Research Council , Cambridge, United Kingdom
            deptResearch Institute for the Environment and Livelihoods , Charles Darwin University , Darwin, Australia
            deptSoutheast Fisheries Science Center , NOAA/National Marine Fisheries Service , Panama City, United States
            deptShark Advocates International , The Ocean Foundation , Washington, DC, United States
            National Institute of Water and Atmospheric Research , Wellington, New Zealand
            deptGlobal Species Programme , International Union for the Conservation of Nature , Cambridge, United Kingdom
            deptCentre for Sustainable Tropical Fisheries and Aquaculture , James Cook University , Townsville, Australia
            deptSchool of Earth and Environmental Sciences , James Cook University , Townsville, Australia
            deptFlorida Program for Shark Research, Florida Museum of Natural History , University of Florida , Gainsville, United States
            deptIUCN Species Programme Species Survival Commission , Old Dominion University , Norfolk, United States
            deptConservation International Global Marine Species Assessment , Old Dominion University , Norfolk, United States
            deptShark Research Center, Iziko , South African Museum , Cape Town, South Africa
            deptPacific Shark Research Center , Moss Landing Marine Laboratories , Moss Landing, United States
            deptSchool of Earth and Environmental Sciences , Australian Institute of Marine Science , Townsville, Australia
            deptGlobal Marine Species Assessment, Biodiversity Assessment Unit, IUCN Species Programme , Conservation International , Arlington, United States
            deptMarine and Atmospheric Research , Commonwealth Scientific and Industrial Research Organisation , Hobart, Australia
            Max Planck Institute for Chemical Ecology , Germany
            Max Planck Institute for Chemical Ecology , Germany
            Author notes
            [* ]For correspondence: dulvy@ 123456sfu.ca
            Contributors
            Role: Reviewing editor,
            Max Planck Institute for Chemical Ecology , Germany
            Journal
            eLife
            eLife
            eLife
            eLife
            eLife Sciences Publications, Ltd
            2050-084X
            21 January 2014
            2014
            : 3
            24448405 3897121 00590 10.7554/eLife.00590

            This is an open-access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.

            Product
            Funding
            Funded by: Conservation International;
            Award Recipient :
            Funded by: Packard Foundation;
            Award Recipient :
            Funded by: Save Our Seas Foundation;
            Award Recipient :
            Funded by: UK Department of Environment and Rural Affairs;
            Award Recipient :
            Funded by: US State Department;
            Award Recipient :
            Funded by: US Department of Commerce;
            Award Recipient :
            Funded by: Marine Conservation Biology Institute;
            Award Recipient :
            Funded by: Pew Marine Fellows Program;
            Award Recipient :
            Funded by: Mohamed bin Zayed Species Conservation Foundation;
            Award Recipient :
            Funded by: Zoological Society of London;
            Award Recipient :
            Funded by: Canada Research Chairs Program;
            Award Recipient :
            Funded by: Natural Environment Research Council, Canada;
            Award Recipient :
            Funded by: Tom Haas and the New Hampshire Charitable Foundation;
            Award Recipient :
            Funded by: Oak Foundation;
            Award Recipient :
            Funded by: Future of Marine Animal Populations, Census of Marine Life;
            Award Recipient :
            Funded by: IUCN Centre for Mediterranean Cooperation;
            Award Recipient :
            Funded by: UK Joint Nature Conservation Committee;
            Award Recipient :
            Funded by: National Marine Aquarium, Plymouth UK;
            Award Recipient :
            Funded by: New England Aquarium Marine Conservation Fund;
            Award Recipient :
            Funded by: The Deep, Hull, UK;
            Award Recipient :
            Funded by: Blue Planet Aquarium, UK;
            Award Recipient :
            Funded by: Chester Zoo, UK;
            Award Recipient :
            Funded by: Lenfest Ocean Program;
            Award Recipient :
            Funded by: WildCRU, Wildlife Conservation Research Unit, University of Oxford, UK;
            Award Recipient :
            Funded by: Institute for Ocean Conservation Science, University of Miami;
            Award Recipient :
            Funded by: Flying Sharks;
            Award Recipient :
            The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
            Categories
            Research Article
            Ecology
            Custom metadata
            2
            One-quarter of the Chondrichthyes have an elevated risk of extinction, mainly as a result of overfishing.

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