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      Both cetaceans in the Brazilian Amazon show sustained, profound population declines over two decades

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          Abstract

          Obligate river dolphins occur only in the rivers of Asia and South America, where they are increasingly subject to damaging pressures such as habitat degradation, food competition and entanglement in fishing gear as human populations expand. The Amazon basin hosts two, very different, dolphins—the boto or Amazon river dolphin ( Inia geoffrensis) and the smaller tucuxi ( Sotalia fluviatilis). Both species have wide geographical ranges and were once considered to be relatively abundant. Their IUCN Red List conservation status of Data Deficient (DD), due to limited information on threats, ecology, population numbers and trends, did not initially cause alarm. However, the development of dolphin hunting to provide fish bait at around the beginning of this millennium broadly coincided with the onset of a widespread perception that numbers of both species were in decline. Consequently, the need for population trend data to inform conservation advice and measures became urgent. This paper presents a 22-year time series of standardised surveys for both dolphins within the Mamirauá Reserve, Amazonas State, Brazil. Analysis of these data show that both species are in steep decline, with their populations halving every 10 years (botos) and 9 years (tucuxis) at current rates. These results are consistent with published, independent information on survival rates of botos in this area, which demonstrated a substantial drop in annual survival, commencing at around the year 2000. Mamirauá is a protected area, and is subject to fewer environmental pressures than elsewhere in the region, so there is no reason to suspect that the decline in dolphins within the Reserve is more pronounced than outside it. If South America's freshwater cetaceans are to avoid following their Asian counterparts on the path to a perilous conservation status, effective conservation measures are required immediately. Enforcement of existing fishery laws would greatly assist in achieving this.

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          First human-caused extinction of a cetacean species?

          The Yangtze River dolphin or baiji (Lipotes vexillifer), an obligate freshwater odontocete known only from the middle-lower Yangtze River system and neighbouring Qiantang River in eastern China, has long been recognized as one of the world's rarest and most threatened mammal species. The status of the baiji has not been investigated since the late 1990s, when the surviving population was estimated to be as low as 13 individuals. An intensive six-week multi-vessel visual and acoustic survey carried out in November-December 2006, covering the entire historical range of the baiji in the main Yangtze channel, failed to find any evidence that the species survives. We are forced to conclude that the baiji is now likely to be extinct, probably due to unsustainable by-catch in local fisheries. This represents the first global extinction of a large vertebrate for over 50 years, only the fourth disappearance of an entire mammal family since AD 1500, and the first cetacean species to be driven to extinction by human activity. Immediate and extreme measures may be necessary to prevent the extinction of other endangered cetaceans, including the sympatric Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientalis).
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            River dolphins and flooded forest: seasonal habitat use and sexual segregation of botos (Inia geoffrensis) in an extreme cetacean environment

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              Conflicts with fisheries and intentional killing of freshwater dolphins (Cetacea: Odontoceti) in the Western Brazilian Amazon

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                Author and article information

                Contributors
                Role: ConceptualizationRole: Data curationRole: Funding acquisitionRole: MethodologyRole: Project administrationRole: ResourcesRole: Writing – original draftRole: Writing – review & editing
                Role: Formal analysisRole: Writing – original draftRole: Writing – review & editing
                Role: Writing – original draftRole: Writing – review & editing
                Role: ConceptualizationRole: Funding acquisitionRole: MethodologyRole: ResourcesRole: Writing – original draftRole: Writing – review & editing
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, CA USA )
                1932-6203
                2 May 2018
                2018
                : 13
                : 5
                : e0191304
                Affiliations
                [1 ] Laboratório de Mamíferos Aquáticos, Coordenação de Biodiversidade, Instituto Nacional de Pesquisas da Amazônia, Manaus, Amazonas, Brazil
                [2 ] Departamento de Ciências Pesqueiras, Faculdade de Ciências Agrárias, Universidade Federal do Amazonas, Manaus, Amazonas, Brazil
                [3 ] Centre for Remote Environments, University of Dundee, Dundee, Scotland, United Kingdom
                Sanya Institute of Deep-sea Science and Engineering Chinese Academy of Sciences, CHINA
                Author notes

                Competing Interests: The authors have declared that no competing interests exist.

                Author information
                http://orcid.org/0000-0002-1774-0393
                Article
                PONE-D-17-30732
                10.1371/journal.pone.0191304
                5931465
                29718917
                0b525a02-d016-4eaa-ba76-e8f2375b71dd
                © 2018 F. da Silva et al

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 20 August 2017
                : 1 January 2018
                Page count
                Figures: 3, Tables: 2, Pages: 12
                Funding
                Projeto Boto receives the sponsorship of the AMPA/Petrobras Ambiental Program, INPA/MCTIC and by the AMPA/MPF-TC No. 02/2015-TAC, No. 003/2014. RLD received an INPA/PCI scholarship during part of the study. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Categories
                Research Article
                Biology and Life Sciences
                Organisms
                Eukaryota
                Animals
                Vertebrates
                Amniotes
                Mammals
                Marine Mammals
                Dolphins
                Biology and Life Sciences
                Marine Biology
                Marine Mammals
                Dolphins
                Earth Sciences
                Marine and Aquatic Sciences
                Marine Biology
                Marine Mammals
                Dolphins
                Earth Sciences
                Marine and Aquatic Sciences
                Bodies of Water
                Rivers
                Ecology and Environmental Sciences
                Aquatic Environments
                Freshwater Environments
                Rivers
                Earth Sciences
                Marine and Aquatic Sciences
                Aquatic Environments
                Freshwater Environments
                Rivers
                Earth Sciences
                Marine and Aquatic Sciences
                Bodies of Water
                Lakes
                Ecology and Environmental Sciences
                Aquatic Environments
                Freshwater Environments
                Lakes
                Earth Sciences
                Marine and Aquatic Sciences
                Aquatic Environments
                Freshwater Environments
                Lakes
                People and places
                Geographical locations
                South America
                Brazil
                Earth Sciences
                Hydrology
                Surface Water
                Biology and Life Sciences
                Organisms
                Eukaryota
                Animals
                Vertebrates
                Fish
                Freshwater Fish
                Ecology and Environmental Sciences
                Aquatic Environments
                Freshwater Environments
                Fresh Water
                Earth Sciences
                Marine and Aquatic Sciences
                Aquatic Environments
                Freshwater Environments
                Fresh Water
                Biology and Life Sciences
                Agriculture
                Fisheries
                Custom metadata
                All relevant data are within the paper and its Supporting Information files.

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