Data from: Historical data to plan the recovery of the European eel

1. Long-term perspectives are critical to understand contemporary ecological systems. However, historical data on the distribution of biodiversity have only rarely been used in applied environmental sciences. 2. Here, we use historical sources to reconstruct the historical range of the European eel, a critically endangered species. We then use this baseline range to set range targets for the recovery of the European eel, as opposed to the abundance-based targets established by the European Union, which are constrained by the poor information on pre-collapse stocks. 3. We collected over 10 000 historical freshwater fish records from Spain in the 19th and 16th centuries, as well as over 25 000 records from the global biodiversity information facility (GBIF) to characterize historical and current European eel distribution in the Iberian Peninsula. We converted fish records into an eel presence–absence data set using subcatchment as spatial unit of analysis and modelled eel distribution in the different historical periods. 4. The eel was historically widespread throughout the Iberian Peninsula, but it has lost over 80% of its original range, mainly due to river fragmentation by dams. Distribution models applied to 16th- and 19th-century data showed a high agreement, supporting the use of the 19th-century estimated distribution as a baseline range. We identified the number and identity of dams that should be made passable for accomplishing specific range recovery targets, for example showing that acting upon 20 dams would make available 60% of the baseline eel range. 5. Synthesis and applications. This work exemplifies how insights gained from historical ecology can support and guide present-day management of migratory fishes. Similar approaches could be developed throughout Europe to plan the recovery of the eel, since there are large amounts of historical eel records. Historical baseline ranges for the eel range should be incorporated into the European Union legal mandates aimed at the recovery of the species.

1. 长期视角对于理解当代生态系统至关重要，然而生物多样性分布的历史数据极少被应用于应用环境科学研究中。
2. 本研究依托历史文献资料，重构了极危物种欧洲鳗鲡的历史分布范围。随后以此基准分布范围为参照，为欧洲鳗鲡的种群恢复设定分布范围目标——这与欧洲联盟（European Union）制定的基于种群丰度的恢复目标有所不同，后者受限于崩溃前种群资源的信息匮乏。
3. 研究收集了16世纪与19世纪西班牙境内逾10000条历史淡水鱼类记录，同时从全球生物多样性信息设施（Global Biodiversity Information Facility, GBIF）获取超25000条相关记录，以此刻画伊比利亚半岛欧洲鳗鲡的历史与当前分布格局。本研究以子汇水区（subcatchment）作为空间分析单元，将鱼类记录转换为鳗鲡出现-缺失（presence-absence）数据集，并对不同历史时期的鳗鲡分布开展建模分析。
4. 历史上欧洲鳗鲡广泛分布于整个伊比利亚半岛，但目前其原有分布范围已缩减超80%，这一变化主要源于大坝造成的河流破碎化。针对16世纪与19世纪数据构建的分布模型一致性较高，证实了以19世纪估算的分布范围作为基准分布范围的合理性。本研究还明确了为实现特定分布恢复目标所需打通洄游通道的大坝数量与具体点位——例如，仅对20座大坝开展改造，即可恢复60%的基准鳗鲡分布范围。
5. 综合与应用：本研究阐明了历史生态学的研究结论如何支撑并指导当前洄游鱼类的管理工作。鉴于欧洲境内留存有大量欧洲鳗鲡的历史记录，类似研究方法可在全欧范围内推广，用于规划欧洲鳗鲡的种群恢复工作。欧洲鳗鲡分布范围的历史基准值，应当纳入欧洲联盟（European Union）旨在恢复该物种种群的法定管理框架之中。