Data from: Response of a pan-European fish index (EFI+) to multiple pressures in rivers across Spain

Rivers are ecosystems highly threatened by human activities and fish are an invaluable tool to measure and communicate environmental degradation and restoration. Fish bioassessment is crucial but notoriously difficult in Mediterranean-climate streams for a number of reasons, including low local species richness, faunas with high spatial turnover and generalist species, and scarcity of reference sites. In this study, we conducted the most comprehensive test of the pan-European fish index (EFI+) in the Iberian Peninsula, analysing its response to multiple anthropogenic pressures. We compiled a database, which we provide online, with 2970 electrofishing samples across Spain, involving 100,732 fish of 69 species. Principal component analyses of many quantitative variables were used to create new synthetic anthropogenic pressure indices. Correlation and multiple linear regression analyses were used to test the relationship between these pressures and the fish index (EFI+) and its four individual metrics scores (i.e., density of species intolerant to oxygen depletion, density of fish ≤150 mm of species intolerant to habitat degradation, richness of species of rheophilic reproduction habitat, and density of species of lithophilic reproduction habitat). We also obtained the same models but including the river basin district to test for spatial or methodological differences. Our results indicate that both the EFI+ index and its individual metrics respond to various anthropogenic pressures. These pressures explained about 36% of the variance of EFI+ values. Notably, downstream and mainstream reaches with higher agricultural or urban land uses, increased hydrologic alteration, and water and habitat quality impairment exhibited lower EFI+values. Although less variance was explained for the individual metrics than for the fish index, they responded as expected to the different pressures. For instance, the richness of rheophilic species and the number of lithophilic fish decreased with hydrologic alteration, while the number of fish intolerant to oxygen depletion decreased with water quality impairment. Similar correlations were observed when river basin district was included in the model, but with higher explained variation and greater significance of the pressures. While it is possible to develop regional indices with more metrics and a stronger correlation with anthropogenic pressures, EFI+ is the only fish index that has been validated throughout the Spanish peninsular territory. Our results support the use of EFI+ in intercalibrationexercises across Spain until better regional indices are developed.

河流是受人类活动高度威胁的生态系统，而鱼类是衡量与传递环境退化及修复成效的珍贵工具。鱼类生物评估至关重要，但在地中海气候溪流中开展此类工作却极具挑战性，原因诸多：本地物种丰富度偏低、动物区系空间周转速率高且多为广适性物种，以及参照位点稀缺。本研究针对伊比利亚半岛开展了泛欧洲鱼类指数（EFI+）迄今最全面的验证测试，分析其对多重人为压力的响应。我们构建了公开在线数据库，涵盖西班牙境内2970份电捕鱼（electrofishing）采样样本，涉及69个物种的100732尾鱼类。研究采用多定量变量的主成分分析，构建了全新的合成人为压力指数；通过相关性分析与多元线性回归，检验了上述压力与鱼类指数（EFI+）及其四项单项指标得分的关联关系：四项指标分别为对溶氧耗竭不耐受的物种密度、体长≤150mm且对生境退化不耐受的鱼类密度、喜流性繁殖物种丰富度，以及喜石性繁殖物种密度。我们还构建了纳入流域分区的同类模型，以检验空间或方法学差异的影响。结果显示，EFI+指数及其单项指标均对各类人为压力存在响应。此类压力可解释约36%的EFI+值变异。值得注意的是，农业或城镇用地占比更高的下游及干流河段、水文扰动加剧的区域，以及水质与生境质量受损的区域，其EFI+值普遍偏低。尽管单项指标的变异解释度低于整体鱼类指数，但它们均按预期对不同压力产生了响应：例如，喜流性物种丰富度与喜石性鱼类密度随水文扰动加剧而下降，而对溶氧耗竭不耐受的物种密度则随水质恶化而降低。当模型纳入流域分区后，观测到了相似的相关性，但变异解释度与压力因子的显著性均有所提升。尽管可开发纳入更多指标、与人为压力相关性更强的区域指数，但EFI+是目前唯一在西班牙全境范围内完成验证的鱼类指数。本研究结果支持在西班牙境内的跨区域校准实践中使用EFI+，直至更完善的区域指数得以开发。