1. This paper describes the tensions between the legal requirements for conservation and the most beneficial biological practice for mobile transnational marine species, using the harbour porpoise (Phocoena phocoena) in European Atlantic waters as a case study.
2. Harbour porpoise are the smallest and one of the most abundant cetaceans occurring throughout the European continental shelf waters, and are affected by human activities occurring in the same waters, especially certain fishing activities.
3. The Convention on the Conservation of European Wildlife and Natural Habitats (the Bern Convention) and its implementing legislation the Council Directive on the Conservation of Natural Habitats and of Wild Fauna and Flora 92/43/EEC (i.e. the Habitats Directive) are the main legal drivers for species conservation throughout the European Union. They aim for the long-term achievement of favourable conservation status and make provision for the use of two conservation measures: protected areas and strict protection measures. The strict protection measures aim to ensure that all forms of deliberate killing are prevented, and that where incidental killing and capture occurs, it does not have a negative effect on conservation status.
4. The conservation of harbour porpoise is currently dependent upon tackling the key issue of bycatch in fisheries. However, in challenges to Member States on their application of the Habitats Directive, the European Commission has chosen to focus on site designation rather than the implementation of the strict protection measures required to monitor and, where necessary, reduce bycatch.
5. This tension between a legal focus on the designation of protected areas instead of tackling threats such as bycatch has potentially led to negative conservation consequences for harbour porpoise and, in part, may explain why wider marine biodiversity has continued to deteriorate in Europe.

中文翻译：

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跨国物种保护：法律要求与最佳科学证据之间的紧张关系

1. 本文以欧洲大西洋水域的港湾鼠海豚 ( Phocoena phocoena ) 作为案例研究，描述了保护的法律要求与移动跨国海洋物种最有益的生物实践之间的紧张关系。
2. 港湾鼠海豚是整个欧洲大陆架水域中体型最小、数量最丰富的鲸目动物之一，受到在同一水域发生的人类活动，特别是某些捕鱼活动的影响。
3. 《欧洲野生动物和自然栖息地保护公约》（伯尔尼公约）及其执行立法、理事会关于保护自然栖息地和野生动植物群的指令 92/43/EEC（即栖息地指令）是主要的法律整个欧盟物种保护的驱动因素。它们旨在长期实现良好的保护状态，并规定使用两种保护措施：保护区和严格的保护措施。严格的保护措施旨在确保防止各种形式的故意杀戮，并且在发生意外杀戮和捕获的情况下，不会对保护状况产生负面影响。
4. 港湾鼠海豚的保护目前取决于解决渔业兼捕的关键问题。然而，在成员国在应用栖息地指令方面面临的挑战时，欧盟委员会选择将重点放在指定地点，而不是实施监测和必要时减少兼捕所需的严格保护措施。
5. 将法律重点放在指定保护区而不是解决兼捕等威胁之间的这种紧张关系可能会对港湾鼠海豚的保护产生负面影响，并且在一定程度上可以解释为什么更广泛的海洋生物多样性在欧洲继续恶化。