Abstract
South American rivers have become intensely affected by the construction of hydroelectric dams that block the river’s connectivity for migratory fish species. In order to mitigate the problems caused by dams and to reestablish connections between habitats, fishways are implemented. Fishways are structures that aid fish in overcoming obstacles and help preserve migratory, reproductive, and feeding routes. This study performed an inventory of all hydropower plants—present and future—in the Upper Paraná River, with the objective of identifying fishways unknown to scientific literature, as well as the task of mapping them. By doing so, the current situation of structural connectivity via fishways in the Upper Paraná River Basin was described. Overall, 389 dams along 209 rivers were identified; of these, only 9% (35 dams) have fishways. In addition, an alarming explosion of future medium-sized hydropower plants was observed, with an expectation of an almost 500% increase in relation to those existing. This data reveals a trend of reduction of free-flowing river stretches, which are crucial habitats for Neotropical potamodromous species, and point to a deficiency in the structural connectivity of existing hydropower dams. Furthermore, if the implementations of these expected constructions are associated with limited connectivity as a result of the absence of fishways, the management of fisheries and their resources in the Upper Paraná River may become unsustainable.
Highlights
The great rivers of South America have been highly fragmented by hydroelectric dams in order to meet an ever-growing energy demand [1]
The fragmentation of rivers caused by dams is one of the leading factors of population decline in fish species [4]
It is possible that this elevated number of medium-sized dams is the result of an exhaustion of the great hydraulic potentials caused by the construction of large-sized hydropower plants (UHEs) within the last 50 years [1]
Summary
The great rivers of South America have been highly fragmented by hydroelectric dams in order to meet an ever-growing energy demand [1] The construction of such dams is one of many anthropic actions which result in the greatest impact on hydrographic basins [2]. Among such impacts is the regulation of the river flow, which alters nutrient dynamics [3], fragments the ecosystem, changes the morphology of water bodies [4], and promotes the longitudinal imbalance of the rivers [5], which greatly decreases biodiversity and leads to the loss of biological and genetic resources [2,6,7]. Several different management strategies, such as stocking programs and construction of fish passes [19], have been attempted in order to improve the sustainability of artisanal fishery and the social conditions of families who are dependent on this resource
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