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      Diagnosing the dangerous demography of manta rays using life history theory

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          Abstract

          Background. The directed harvest and global trade in the gill plates of mantas, and devil rays, has led to increased fishing pressure and steep population declines in some locations. The slow life history, particularly of the manta rays, is cited as a key reason why such species have little capacity to withstand directed fisheries. Here, we place their life history and demography within the context of other sharks and rays.

          Methods. Despite the limited availability of data, we use life history theory and comparative analysis to estimate the intrinsic risk of extinction (as indexed by the maximum intrinsic rate of population increase r max) for a typical generic manta ray using a variant of the classic Euler–Lotka demographic model. This model requires only three traits to calculate the maximum intrinsic population growth rate r max: von Bertalanffy growth rate, annual pup production and age at maturity. To account for the uncertainty in life history parameters, we created plausible parameter ranges and propagate these uncertainties through the model to calculate a distribution of the plausible range of r max values.

          Results. The maximum population growth rate r max of manta ray is most sensitive to the length of the reproductive cycle, and the median r max of 0.116 year −1 95th percentile [0.089–0.139] is one of the lowest known of the 106 sharks and rays for which we have comparable demographic information.

          Discussion. In common with other unprotected, unmanaged, high-value large-bodied sharks and rays the combination of very low population growth rates of manta rays, combined with the high value of their gill rakers and the international nature of trade, is highly likely to lead to rapid depletion and potential local extinction unless a rapid conservation management response occurs worldwide. Furthermore, we show that it is possible to derive important insights into the demography extinction risk of data-poor species using well-established life history theory.

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          R: A language and environment for statistical computing

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            International trade drives biodiversity threats in developing nations.

            Human activities are causing Earth's sixth major extinction event-an accelerating decline of the world's stocks of biological diversity at rates 100 to 1,000 times pre-human levels. Historically, low-impact intrusion into species habitats arose from local demands for food, fuel and living space. However, in today's increasingly globalized economy, international trade chains accelerate habitat degradation far removed from the place of consumption. Although adverse effects of economic prosperity and economic inequality have been confirmed, the importance of international trade as a driver of threats to species is poorly understood. Here we show that a significant number of species are threatened as a result of international trade along complex routes, and that, in particular, consumers in developed countries cause threats to species through their demand of commodities that are ultimately produced in developing countries. We linked 25,000 Animalia species threat records from the International Union for Conservation of Nature Red List to more than 15,000 commodities produced in 187 countries and evaluated more than 5 billion supply chains in terms of their biodiversity impacts. Excluding invasive species, we found that 30% of global species threats are due to international trade. In many developed countries, the consumption of imported coffee, tea, sugar, textiles, fish and other manufactured items causes a biodiversity footprint that is larger abroad than at home. Our results emphasize the importance of examining biodiversity loss as a global systemic phenomenon, instead of looking at the degrading or polluting producers in isolation. We anticipate that our findings will facilitate better regulation, sustainable supply-chain certification and consumer product labelling.
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              Uncertainty, resource exploitation, and conservation: lessons from history.

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                Author and article information

                Contributors
                Journal
                PeerJ
                PeerJ
                PeerJ
                PeerJ
                PeerJ
                PeerJ Inc. (San Francisco, USA )
                2167-8359
                27 May 2014
                2014
                : 2
                : e400
                Affiliations
                [1 ]Earth to Ocean Research Group, Department of Biological Sciences, Simon Fraser University , Burnaby, British Columbia, Canada
                [2 ]Centre for Sustainable Tropical Fisheries and Aquaculture & School of Earth and Environmental Sciences, James Cook University , Townsville, Australia
                [3 ]NOAA/National Marine Fisheries Service, Southeast Fisheries Science Center , Panama City, FL, USA
                Article
                400
                10.7717/peerj.400
                4045333
                24918029
                0ee14eb2-b912-41ce-85c5-56e9eacb7d05
                © 2014 Dulvy et al.

                This is an open access article, free of all copyright, made available under the Creative Commons Public Domain Dedication. This work may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose.

                History
                : 20 December 2013
                : 7 May 2014
                Funding
                Funded by: Natural Science and Engineering Research Council, Canada
                Funded by: Canada Research Chairs program
                Funded by: Save Our Seas Foundation project
                Award ID: #235
                Funded by: US State Department Contribution to IUCN
                We thank the Natural Science and Engineering Research Council, Canada (NKD, SAP), the Canada Research Chairs program (NKD), Save Our Seas Foundation project #235 (NKD) and the US State Department contribution to IUCN (NKD) for funding. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Opinions expressed herein are of the authors only and do not imply endorsement by any agency or institution associated with the authors.
                Categories
                Aquaculture, Fisheries and Fish Science
                Conservation Biology
                Ecology
                Marine Biology
                Science Policy

                cites,data-poor fisheries,life history invariant,wildlife trade,euler–lotka,population growth rate,accounting for uncertainty,von bertalanffy growth function,ocean ivory,chinese medicine

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