Genetic Diversity of the Surubim-Do-Iguaçu, a Giant Catfish Species Threatened with Extinction: Recommendations for Species Conservation

Steindachneridion melanodermatum is the largest catfish of the Lower Iguaçu River and is endangered due to the habitat fragmentation caused by dams. Currently, the wild population’s last refuge is restricted to an area of 190 km. This study presents the first analysis of its genetic diversity and population structure, using microsatellite loci and mtDNA. The population has an adequate level of genetic diversity, but signs of a recent bottleneck were observed. The Baixo Iguaçu Hydroelectric Power Plant has recently fragmented the population and threatened it with extinction in a reduced area of nearly 30 km. Based on our results, we strongly advise against the stocking of breeding specimens below the Salto Caxias HPP to not compromise the integrity of the native gene pools at the receptor sites. In addition, we recommend manual fish transposition, trap-and-haul, to maintain the genetic connectivity of individuals upstream and downstream of the dam as a conservation strategy. Furthermore, studies on behavior and swimming capacities, and suitable fishways for this species must be developed. We strongly recommend that the Lower Iguaçu River and its tributaries be protected and preserved as free from additional barriers to prevent future habitat disruption for the benefit of S. melanodermatum and several other endemic and endangered species.

Deep Pools: Ecological Sanctuaries for Steindachneridion melanodermatum, a Large Endemic and Endangered Pimelodid of the Iguaçu River

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.

Ichthyofauna in the last free-flowing river of the Lower Iguaçu basin: the importance of tributaries for conservation of endemic species

The fish fauna from the Lower Iguaçu River and tributaries upstream of the Iguaçu Falls, the last free-flowing river stretch, were investigated. Twenty five sites in tributaries and the main channel were sampled between 2010 and 2016 using several kinds of fishing gear. The species were categorized according to their size, origin, and conservation status. Species richness and abundance in the main channel and tributaries were compared. In total, 87,702 specimens were recorded, comprising 76 species, 25 families, 53 genera, and eight orders. Characiformes and Siluriformes were the richest orders, representing 92% of the total specimens; Characidae, Cichlidae, Pimelodidae, and Loricariidae were the richest families. The fish fauna was composed of small and medium-sized species and included endemic (42%), autochthonous (24%), allochthonous (21%), and exotic (9%) species, as well as hybrids (4%). Significant differences in the relative numerical abundance of species were found among sites. Ancistrus mullerae and Rhamdia branneri (endemic) were indicator species for tributaries inside of Iguaçu National Park (INP), while Phalloceros harpagos (autochthonous) and Ictalurus punctatus (exotic) for tributaries outside of INP and Odontesthes bonariensis (allochthonous) for the main channel. The last dam-free stretch of the Lower Iguaçu River and tributaries upstream the Iguaçu Falls exhibits a rich endemic fish fauna, including some rare, endangered species (Steindachneridion melanodermatum, Gymnogeophagus taroba, and Psalidodon gymnogenys). These findings are essential to predict and understand the effects caused by the new Baixo Iguaçu Hydroelectric Power Plant and highlight the importance of tributaries and Iguaçu National Park for conservation of endemic species.

Kaolinite deposits in the upper Iguaçu river, Brazil: formation and mineralogical attributes

Kaolinite (Kt) is the most studied mineral, being widely used in the ceramic, pharmaceutical and cellulose industries, in addition to being the main soil mineral in the world. Found in different parts of the planet, it differs in genesis and may be formed as a result of local weathering of the rocks, occurring in the silt fraction; and also due to the mineral's neogenesis with a predominance of clay-sized particles. The plain of upper Iguaçu river has the largest kaolinitic deposit in the south of Brazil and it’s formation raised doubts if this kaolin was transported or formed in situ due the high organic matter in the alluvial plain. To elucidate the origin of kaolin deposits, we sampled a possible font of the mineral, in the mountains of Serra do Mar and sampled two tubes that reach 4 m depth in the upper Iguaçu plain. We performed textural analysis, organic carbon, X-ray diffraction, Kt crystallography in silt and clay fractions, thermal analysis (TDA/TG) to quantify Kt and Gb in the clay fraction and scanning electron microscopy (SEM) with dispersive energy spectroscopy (EDS). The TDA/TG analysis demonstrated that saprolite has 66% of the kaolinite found in the plain. The XRD analysis shows a significant presence of mica (Mc) in all samples of the silt fraction, both in Serra do Mar and in the plain. In SEM/EDS, crystals with planar growth are observed, and the presence of pseudomorphic Mc-Kt in the silt fraction of all analyzed samples, with emphasis on the tubes sample with the crystal having almost twice the size of that observed in the saprolite sample from Serra do Mar, allowing to infer that the Kt of the silt fraction of the wetland soils were formed on site by the diagenesis of mica particles. The results obtained in this work indicate that the kaolinitic material found in the wetland of the upper Iguaçu plain is the result of weathering processes in the wetland itself, evidenced by the large pseudomorphs found, even greater than those observed in Serra do Mar.