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.

Steindachneridion melanodermatum, an endemic and endangered species, is the largest catfish in the Lower Iguaçu River basin. Currently, the wild population of this species no longer exists in most of this basin, probably due to the loss of habitat by successive hydroelectric dams. This study evaluated the spatial distribution and abundance of S. melanodermatum in the last free-flowing river stretch of approximately 190 km downstream from the Salto Caxias Dam, upstream of the Iguaçu Falls, as well as some tributaries. Hydroacoustic and fishing campaigns were performed between September 2010 to December 2016 to characterize the preferred habitat. A total of 180 specimens was sampled with higher abundances in a protected area near Iguaçu Falls in the Iguaçu National Park. Twenty-four deep pools were identified with maximum depths ranging from 5 to 25 m: 21 pools were along the main channel of the Iguaçu River, and three pools were in tributaries. Deep pools are preferential habitats for this species, especially the deep pool called Poço Preto (P23) and its surroundings. Conservation strategies are required to protect these habitats and prevent S. melanodermatum from becoming extinct, such as establishing deep pools as ecological sanctuaries, intensifying the inspection of illegal fishing, and maintaining dam-free tributaries.

The land use and occupation in watersheds directly influences the water resources, and the vegetation cover is a crucial factor for water maintenance. The objective of this study was to characterize the land use and occupation in nine watersheds of the Lower Iguaçu River (Andrada, Monteiro, Gonçalves Dias, Floriano, Silva Jardim, Cotejipe, Sarandi, Capanema and Santo Antônio sub-basin rivers), using the classification from satellite images. The classification area obtained high accuracy (Kappa coefficient of 99.4 to 99.9%). The Floriano River sub-basin presented the highest degree of environmental preservation, followed by Silva Jardim and Gonçalves Dias River sub-basins, fully or partially inserted in Iguaçu National Park. Monteiro and Sarandi river sub-basins showed the smallest areas of vegetation, and Capanema, Cotejipe, Andrada and Santo Antônio River sub-basins exhibited an intermediate condition. This tendency was verified by the cluster analysis. These results can serve as a baseline for planning, monitoring and management of this area, environmental modeling, conservation of water resources, biodiversity, and environmental services.

O conhecimento da morfometria, do relevo e rede de drenagem bacias hidrográficas é importante para a gestão ambiental. Portanto, este estudo visa caracterizar a morfometria e identificar as características do relevo em nove bacias hidrográficas afluentes do rio Iguaçu. A caracterização de vertentes, rede de drenagem e declividade foi realizada utilizando um Modelo Digital de Terreno (MDT) e os dados obtidos foram comparados visualmente aos resultados das cartas topográficas da Agência Nacional de Águas (ANA) (2015). As bacias analisadas apresentaram de maneira geral formas alongadas, sendo pouco suscetíveis à enchentes, com relevo ondulado, possuem drenagem intermediária a pobre e sinuosidade de intermediária a alta. Os resultados obtidos se assemelham aos obtidos pela ANA (2015), baseados em escalas menores. As hierarquias para cada bacia foram satisfatórias, assim como a metodologia utilizada, pois não requer a utilização de máquinas sofisticadas para a sua execução, e resulta em dados confiáveis com pouca perda de precisão. Os resultados são inéditos para essas bacias e as variáveis geomorfológicas estimadas podem apoiar a tomada de decisão tanto em relação aos riscos das atividades antrópicas quanto para a definição de áreas de conservação, especialmente de áreas de interesse para a conservação da água e dos ecossistemas aquáticos.

The hydrographic basin of Arroio Marreco (Paraná State) concentrates a productive chain of fish farming and great intensification of tilapia farming. In this study, we aimed to monitor the quality of effluent water and organic and inorganic elements released by fish farming in ponds, using geomorphological and land-use and occupation data. The Terrain Analysis Using Digital Elevation Models, Digital Elevation Model software was used to delimit watersheds in the software Quantum geographic information system version 3.6.3. A total of 1,457 production units (water slides) were identified across the study area. This represented an occupied area of 160.2 ha. Analyzing the sub-basins, it was found that High Marreco is the sub-basin with the most developed logistical chain. Low Marreco does not yet have an integration of its fish farming with the region’s logistics chain. Medium Marreco does not have fish farming as its main activity, only using it to reuse inputs from other agricultural activities. There is a large input of nutrients from aquaculture in all the sub-basins. To reduce them, it is recommended to implement decantation and/or reuse of wastewater systems. The results of this study show how important it is to know the dynamics of nutrients in the fish farms and the physical characteristics of the drainage basin to determine the support capacity of the environment, so as not to allow licenses that promote impacts above the self-cleaning capacity of the courses water.