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

Abstract

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.

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

“…The study area comprised the last free-flowing river stretch of the Lower Iguaçu basin, which is approximately 190 km long from downstream of the Salto Caxias Dam (1240 MW) to upstream of the Iguaçu Falls (Figure 1) and exhibits diverse landscape characteristics [37]. In this stretch, the Iguaçu River is embedded with a rocky bed consisting of magnetic basaltic rock that originated in the Mesozoic and presents the remaining fragments of the Atlantic Forest biome.…”

“…The last refuge of the wild population of S. melanodermatum is the 190 km long damfree stretch of the Iguaçu River and its tributaries, which extend downstream from the Salto Caxias Dam to the Iguaçu Falls [36]. The region exhibits diverse landscape characteristics, from a protected area, namely, the Iguaçu National Park (INP), to anthropized ones [37]. The establishment of management and conservation plans for S. melanodermatum is crucial because of the upcoming threats to its conservation [37].…”

“…The region exhibits diverse landscape characteristics, from a protected area, namely, the Iguaçu National Park (INP), to anthropized ones [37]. The establishment of management and conservation plans for S. melanodermatum is crucial because of the upcoming threats to its conservation [37]. Some fish species, such as S. melanodermatum, are more vulnerable to environmental degradation since they require specific habitats [38].…”

Here comes the large catfish “jaú” Zungaro jahu (Ihering 1898) (Teleostei, Pimelodidae): a new alarming case of fish introduction in a high-endemism Neotropical ecoregion

“…Acta Limnologica Brasiliensia, 2022, vol. 34, e25 Daga & Gubiani (2012); Daga et al (2016); Mezzaroba et al (2021); Pini et al (2021)]. Unfortunately, the introduction of fish species in this aquatic ecoregion is subsidized by supposed local economic attractions, sport-fishing programs, and even by the proposals of new environmental laws [see Vitule et al (2014); Ribeiro et al (2017); Geller et al (2021a, b)].…”

“…basin) are listed under some international level of threat, i.e., critically endangered, endangered, or vulnerable (Instituto Chico Mendes de Conservação da Biodiversidade, 2018; Standards and Petitions Committee of the IUCN Species Survival Commission, 2022; Mezzaroba et al, 2021). For example, the pimelodid "surubim-do-iguaçu" Steindachneridion melanodermatum Garavello 2005 is categorized as endangered (Instituto Chico Mendes de Conservação da Biodiversidade, 2018) representing the largest native fish of the basin, which nowadays only inhabiting small free-flowing river stretches and deep pools in the Lower Iguaçu River basin (Garavello, 2005;Assumpção et al, 2021a, b;Pini et al, 2021). Here we aim to report the first and alarming occurrence of the non-native catfish "jaú" Zungaro jahu (Ihering 1898) in the Iguaçu River basin above the Iguaçu Falls and discuss the potential ecological consequences on the native and endemic fish fauna of the basin, in particular on species phylogenetically close, as the "surubim-do-iguaçu".…”