Effect of waterfalls and the flood pulse on the structure of fish assemblages of the middle Xingu River in the eastern Amazon basin

Abstract

The structure of fish assemblages in Neotropical rivers is influenced by a series of environmental, spatial and/or temporal factors, given that different species will occupy the habitats that present the most favourable conditions to their survival. The present study aims to identify the principal factors responsible for the structuring of the fish assemblages found in the middle Xingu River, examining the influence of environmental, spatial, and temporal factors, in addition to the presence of natural barriers (waterfalls). For this, data were collected every three months between July 2012 and April 2013, using gillnets of different sizes and meshes. In addition to biotic data, 17 environmental variables were measured. A total of 8,485 fish specimens were collected during the study, representing 188 species. Total dissolved solids, conductivity, total suspended matter, and dissolved oxygen concentrations were the variables that had the greatest influence on the characteristics of the fish fauna of the middle Xingu. Only the barriers and hydrological periods played a significant deterministic role, resulting in both longitudinal and lateral gradients. This emphasizes the role of the connectivity of the different habitats found within the study area in the structuring of its fish assemblages.Keywords: natural barriers, connectivity, hydrological periods, community ecology, impacts of hydroelectric dams. Efeito das cachoeiras e do pulso de inundação na estrutura das assembleias de peixes do Médio Rio Xingu, Amazônia oriental ResumoA estrutura da ictiofauna em rios neotropicais é constantemente influenciada por fatores ambientais, espaciais e/ou temporais, uma vez que as espécies tendem a ocupar ambientes com condições favoráveis à sua sobrevivência. Dessa forma, esta pesquisa tem como objetivo responder qual o principal fator responsável pela estruturação das assembleias de peixes no Médio Rio Xingu, testando a influência dos fatores ambientais, espaciais e temporais, além da presença de barreiras naturais (cachoeiras

A New Multi-Temporal Forest Cover Classification for the Xingu River Basin, Brazil

“…The Xingu River basin encompasses the fourth largest catchment area of the Amazon. It is known for its high fish biodiversity, with an estimated 600 species, 10% of them endemic to this river basin with many remaining to be described [11][12][13][14]. Several ethnic groups inhabit a mosaic of indigenous lands in a large part of the basin, contributing greatly to a slower rate of deforestation than is seen in unprotected Xingu basin headwaters [15][16][17].…”

Population and reproductive parameters of the red-tailed catfish, Phractocephalus hemioliopterus (Pimelodidae: Siluriformes), from the Xingu River, Brazil

“…The predominant vegetation is typical lowland Amazon rainforest (Barbosa et al, 2018). The annual fluviometric variation recorded on the river can be divided into four distinct hydrological periods: the dry (September-November), filling (December-February), flood (March-May), and receding (June-August) (see Barbosa et al, 2015;. The fluviometric data were obtained from the Brazilian National Waters Agency ("Agência Nacional de Águas", ANA, 2018).…”

“…Specimens of P. hemioliopterus were collected quarterly from September 2012 to January 2014, using gillnets of ten different mesh sizes (20-180 mm stretch meshes), and long lines with 30 hooks (sizes 12⁄0 and 14⁄0), cast under the guidance of a local fisherman and set for twelve hours per day (18:00 h to 06:00 h). Fish were sampled according to the environmental monitoring guidelines of the Belo Monte Dam (for further details of the sampling methods, see Barbosa et al, 2015). The specimens captured were measured to determine their standard length (S L ; 0.1 cm), and weighed to establish total mass (T M ; 0.1 g) and gonadal mass (G M ; 0.1 g).…”

Deciphering the many maps of the Xingu – an assessment of land cover classifications at multiple scales

“…A more reliable road system has also opened not only the agrarian frontier (Schmink et al 2019) (Junk et al 1989). The Xingu's natural flood pulse averaged 4.8 m per year (Barbosa et al 2015).…”

“…Based on information compiled from published manuscripts and ichthyological collections, Dagosta and de Pinna (2019) found 502 valid species in the Xingu basin, with 13 of 367 species endemic to lower Xingu and 15 of 333 species endemic to the upper portion of the river. Taking the undescribed species into account, there are an estimated 600 species of fish, 10% of them endemic to the river basin (Camargo et al 2004; Barbosa et al 2015;Giarrizzo et al 2015;Fitzgerald et al 2018;Jézéquel et al 2020a).…”