Fish assemblage in a dammed tropical river: an analysis along the longitudinal and temporal gradients from river to reservoir

Abstract

We analysed changes in the fish assemblage structure along a longitudinal gradient of the Paraíba do Sul River and Funil Reservoir. We tested the hypothesis that shifts from lotic to lentic environment affect the richness and structure of the assemblage which are modulated by seasonal rainfall changes. Standardised monthly samplings were carried out from October 2006 to September 2007 in four zones: 1) river upstream from the reservoir; 2) upper part of the reservoir; 3) lower part of the reservoir, and 4) river downstream from the reservoir. Fishes were caught using gillnets deployed for 15 hours. We collected a total of 4550 specimens, representing 35 species and 5 orders. The highest richness and diversity were recorded in zone 2, the transitional zone between river and reservoir. In this ecotone, lotic and lentic species overlap. Greater abundance and biomass was recorded in the river upstream from the reservoir (zone 1); however, there are no differences between the zones in the structure of assemblages during the wet season. During the dry season, the assemblage structure is more differentiated between zones, although no differences in abundance and biomass occur. The seasonal flow of the river is the major driving factor to influence the fish assemblage structure along the longitudinal gradient from the river to the reservoir.<br>Mudanças na estrutura da assembleia de peixes foram analisadas ao longo de um gradiente longitudinal do rio Paraíba do Sul e Reservatório do Funil. A hipótese testada foi a de que mudanças do ambiente lótico para o lêntico afetam a riqueza e a estrutura da assembleia de peixes que são moduladas pelas variações sazonais da pluviosidade. Coletas mensais padronizadas foram realizadas entre outubro de 2006 e setembro de 2007 em quatro zonas: 1) rio a montante do reservatório; 2) parte alta do reservatório; 3) parte baixa do reservatório, e 4) rio a jusante do reservatório. Os peixes foram capturados com redes de espera que ficaram em operação por 15 horas. Um total de 4.550 espécimes foi coletado, representando 35 espécies e 5 ordens. A maior riqueza e diversidade foram registradas na zona 2, a zona de transição entre rio e reservatório. Neste ecótono, espécies lóticas e lênticas se sobrepõem. Maior abundância e biomassa foram observadas no rio a montante do reservatório (zona 1), no entanto, não houve diferenças na estrutura da assembleia de peixes entre as zonas durante a estação chuvosa. Durante a estação seca, a estrutura da assembleia de peixes foi mais diferenciada entre as zonas, porém sem diferenças na abundância e biomassa. O fluxo sazonal do rio é o principal fator a influenciar a estrutura da assembleia de peixes ao longo do gradiente longitudinal rio-reservatório

Influence of limnological zones on the spatial distribution of fish assemblages in three Brazilian reservoirs

“…Large dams create major changes in rivers globally (Dynesius and Nilsson, 1994;Stanford et al, 1996;Hughes et al, 2005) and in Brazil, where there are more than 700 plants operating for power generation (Agostinho et al, 2008). The reservoirs behind dams create discontinuous longitudinal gradients because of changes in hydrology and geomorphology and consequently on the chemical and physical features of rivers (Oliveira et al, 2003;Britto and Carvalho, 2006;Terra et al, 2010).…”

“…This occurs because of intentional and accidental introductions of non-natives to support fisheries and to help control pest organisms, plus the greater environmental tolerances to anthropogenic disturbance of the introduced species (Moyle and Light, 1996;Hughes et al, 2005;Terra et al, 2010).…”

“…These impoundments combine ecological and functional features of both rivers and lakes, so it is possible to find distinct habitats that are more lake-like or river-like in the same reservoir (Søballe and Kimmel, 1987;Terra et al, 2010;Sanches et al, 2016). Usually, the upper part of a reservoir tends to have riverine features, whereas the N o n -c o m m e r c i a l u s e o n l y lower part has lacustrine characteristics (Irz et al, 2002;Terra et al, 2010;Sanches et al, 2016).…”

“…Usually, the upper part of a reservoir tends to have riverine features, whereas the N o n -c o m m e r c i a l u s e o n l y lower part has lacustrine characteristics (Irz et al, 2002;Terra et al, 2010;Sanches et al, 2016). However, the presence of tributaries along the reservoir can reset these patterns somewhat (Sanches et al, 2016).…”

Interannual variations of the fish assemblage in the transitional zone of the Three Gorges Reservoir: persistence and stability

“…Studies on the fish assemblages in reservoirs suggest that transitional zone, which is an ecotone between the river upstream and the lacustrine zone of the reservoir, is important for the management of reservoirs (Carvalho et al 1998;Oliveira et al 2004Oliveira et al , 2005Agostinho et al 2008). The transitional zone has relatively higher fish density and diversity than others possibly by reason of its higher light penetration and primary productivity (Carvalho et al 1998;Oliveira et al 2004;Santos et al 2010;Terra et al 2010). However, one of the characteristics of the transition zone is its dynamic nature (Thornton et al 1990).…”