Can fishways restore river connectivity? A case study using β diversity as a method of assessment

Abstract Aim β diversity was used as an indicator to test the hypothesis that a fishway can increase river connectivity, as a reduction in the value of this metric indicates greater similarity among fish assemblages. Methods Quarterly sampling was performed with gillnets upstream and downstream of the Porto Primavera dam, Upper Paraná Basin, before the opening of the fishway between February 1999 and May 2001, and between February 2003 and May 2005 with the fishway in operation (10 samples per period/site). The correlation between the fish assemblages and sites was verified by applying two Mantel tests (downstream versus upstream before and one equivalent after the fishway) using the distance matrices generated by the Bray‐Curtis index. The β diversity between downstream and upstream was calculated using the Sørensen index for each sample for the comparison of such values before and after the operation of the fishway, which were tested with Asymptotic Wilcoxon-Mann-Whitney Test. To summarize changes in the structure of the fish assemblages between the sites and periods nonmetric multidimensional scaling (NMDS) was applied based on Bray-Curtis dissimilarities, using multi-response permutation procedures (MRPP). Results The Mantel tests showed no correlation between the upstream and downstream assemblages before the operation of the fishway but greater correlation after. β diversity was lower after than before the fishway, representing an increase in similarity between downstream and upstream with the fishway. MRPP analysis indicated that the fish assemblages between the sites differed more than was expected by chance, with smaller divergence between the sampling sites after the fishway (A = 0.08) than before it opened (A = 0.09). Conclusions Although fishways remain an incipient and controversial theme for neotropical fish, the Porto Primavera fishway appears to be effective in terms of the restoration of connectivity.

# 摘要
## 研究目的
本研究以β多样性（β diversity）为指标，验证过鱼道（fishway）可提升河流连通性的假说——该指标数值降低意味着鱼类群落（fish assemblages）间的相似性提升。

## 研究方法
于1999年2月至2001年5月（过鱼道启用前）、2003年2月至2005年5月（过鱼道启用后），在上巴拉那盆地（Upper Paraná Basin）波尔图普里马韦拉大坝（Porto Primavera Dam）的上下游水域，采用刺网（gillnets）开展季度采样，每个时期的每个采样点位均采集10份样本。基于布莱-柯蒂斯指数（Bray-Curtis index）生成距离矩阵，通过两次曼特尔检验（分别对应过鱼道启用前的上下游群落对比、启用后的上下游群落对比），验证鱼类群落与采样点位间的相关性。针对每一份采样样本，采用索伦森指数（Sørensen index）计算上下游区域的β多样性，对比过鱼道启用前后的该类数值，并通过渐近Wilcoxon-Mann-Whitney检验（Asymptotic Wilcoxon-Mann-Whitney Test）进行显著性检验。为总结不同采样点位与时期下鱼类群落结构的变化，基于布莱-柯蒂斯相异度开展非度量多维标度（nonmetric multidimensional scaling, NMDS）分析，并结合多响应置换过程（multi-response permutation procedures, MRPP）进行验证。

## 研究结果
曼特尔检验结果显示，过鱼道启用前，上下游鱼类群落无显著相关性；而启用后，二者相关性显著提升。过鱼道启用后的β多样性低于启用前，表明过鱼道启用后上下游水域的鱼类群落相似性有所提升。多响应置换过程分析表明，不同采样点位间的鱼类群落差异显著高于随机预期水平；过鱼道启用后，采样点位间的群落差异（A=0.08）小于启用前（A=0.09）。

## 研究结论
尽管针对新热带区鱼类而言，过鱼道仍是一个新兴且存在争议的研究主题，但波尔图普里马韦拉大坝的过鱼道在恢复河流连通性方面似乎具备有效性。