In freshwater systems, the abundance and diversity of long-distance migratory fish are limited by the maintenance of longitudinal connectivity and natural flow regimes of rivers. Using a graph-based view of each riverscape, we analyzed the river fragmentation process and overlapped with the probable number of migratory species in each remaining stretch. Applying this methodology in basins, we assess historical and potential scenarios quantifying segment extensions free from dams determining the fish richness based on the available habitat for each species. The highest number of migratory species was observed in fragments longer than 100 km. In the future scenario, there was an increase in the number of fragments, with an increase in the number of stretches shorter than 50 km, inadequate to maintain most of the migratory species. Segments of the highest classification order and located in the longest lotic fragments were considered the most important for the species habitat conservation. Dam construction in these segments could seriously affect the ecological processes at a regional level. The proposed analyses enable to approach basins with high diversity of species and nonsalmonid species, supporting the lack of base data concerning those areas, and determine priorities for studies and conservation.

中文翻译：

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巴西东南部河流破碎化评估及其对洄游鱼类保护的影响

在淡水系统中，远距离洄游鱼类的丰度和多样性受到河流纵向连通性和自然流动状况的维护的限制。使用每个河流景观的基于图形的视图，我们分析了河​​流破碎过程，并与每个剩余河段中可能的迁徙物种数量重叠。在流域中应用这种方法，我们评估历史和潜在场景，量化没有大坝的段扩展，根据每个物种的可用栖息地确定鱼类丰富度。在长度超过 100 公里的碎片中观察到的迁徙物种数量最多。在未来的情景中，碎片数量增加，长度小于 50 公里的延伸数量增加，不足以维持大部分迁徙物种。分类顺序最高的段和位于最长的裂片中的段被认为对物种栖息地保护最重要。这些段的大坝建设可能会严重影响区域层面的生态过程。拟议的分析能够接近物种和非鲑鱼物种高度多样性的流域，支持缺乏关于这些地区的基础数据，并确定研究和保护的优先事项。