Dissecting the illegal ivory trade: an analysis of ivory seizures data.
Dissecting the illegal ivory trade: an analysis of ivory seizures data.
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DOI：
10.1371/journal.pone.0076539
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发表时间：
2013
期刊：
影响因子：
3.7
通讯作者：
Milliken T
中科院分区：
文献类型：
--
作者：
Underwood FM;Burn RW;Milliken T
非法象牙贸易趋势的可靠证据对于为大象提供决策信息非常重要，但由于贸易的隐蔽性，很难获得。大象贸易信息系统是一个全球性的非法象牙缉获报告数据库，拥有唯一广泛的非法贸易信息。然而，缉获数据中固有的偏差使得很难推断出趋势;各国在缉获和报告缉获情况的能力方面存在差异，这些差异无法直接衡量。我们开发了一个新的建模框架，从缉获数据中提供有关非法象牙贸易趋势的定量证据。该框架使用贝叶斯分层潜变量模型，通过确定描述各国之间和一段时间内缉获和报告率变化的代理变量，减少缉获数据中的偏差。模型产生的偏差调整平滑估计的相对趋势，非法象牙活动的原料和工作象牙在三个重量类别。在全球、区域或国家层面上，非法象牙交易的数量由两个指标表示-交易指数-和非法象牙交易的总重量-重量指数。在全球范围内，活动迅速增加，达到16年来的最高水平，从2007年到2011年增加了一倍以上，从1998年到2011年增加了两倍。超过70%的交易指数来自重量小于10公斤的加工象牙，自2007年以来的快速增长主要是由于中国消费量的增加。超过70%的重量指数来自于从中非和东非运往东南亚和东亚的至少100公斤的象牙原料。这些结果将最近关于偷猎率、种群下降和消费趋势的调查结果联系在一起，为国际大象决策提供了详细的证据。
Reliable evidence of trends in the illegal ivory trade is important for informing decision making for elephants but it is difficult to obtain due to the covert nature of the trade. The Elephant Trade Information System, a global database of reported seizures of illegal ivory, holds the only extensive information on illicit trade available. However inherent biases in seizure data make it difficult to infer trends; countries differ in their ability to make and report seizures and these differences cannot be directly measured. We developed a new modelling framework to provide quantitative evidence on trends in the illegal ivory trade from seizures data. The framework used Bayesian hierarchical latent variable models to reduce bias in seizures data by identifying proxy variables that describe the variability in seizure and reporting rates between countries and over time. Models produced bias-adjusted smoothed estimates of relative trends in illegal ivory activity for raw and worked ivory in three weight classes. Activity is represented by two indicators describing the number of illegal ivory transactions – Transactions Index – and the total weight of illegal ivory transactions – Weights Index – at global, regional or national levels. Globally, activity was found to be rapidly increasing and at its highest level for 16 years, more than doubling from 2007 to 2011 and tripling from 1998 to 2011. Over 70% of the Transactions Index is from shipments of worked ivory weighing less than 10 kg and the rapid increase since 2007 is mainly due to increased consumption in China. Over 70% of the Weights Index is from shipments of raw ivory weighing at least 100 kg mainly moving from Central and East Africa to Southeast and East Asia. The results tie together recent findings on trends in poaching rates, declining populations and consumption and provide detailed evidence to inform international decision making on elephants.
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