Structure of fish assemblages along spatial gradients in a deep subtropical reservoir (Itaipu Reservoir, Brazil-Paraguay border)

Abstract

SynopsisWe assessed the structure of the fish assemblages in the Itaipu Reservoir (Parana´River, Brazil-Paraguay) along a longitudinal or river-dam gradient (composed of riverine, transitional and lacustrine zones) and transversal or upstream-downstream gradients of the tributaries (composed of lotic and lentic stretches of tributaries and reservoir shores). We sampled stations distributed along the environmental gradients quarterly during two years. We caught mostly piscivorous, detritivorous and insectivorous fishes. The structure of the whole fish assemblage both at the regional spatial scale and at the zones of each gradient was significantly non-random according to null models and ordination analysis. When the assemblage was broken into groups, the piscivores and detritivores as well as the predators and prey showed significant nonrandom structure whereas the insectivores, omnivores, herbivores, benthophages and mud-eaters showed random structure. The first groups are those that had more species and the last mentioned are those with fewer species. The tributaries varied more in composition among themselves than the reservoir shores, showing a high heterogeneity in the transversal gradient. The most widespread species was the introduced piscivore Plagioscion squamosissimus. The loricariids were most abundant in the lotic and lentic stretches of the tributaries. We also observed temporal variability in species composition, mainly in the reservoir shores possibly due to the influence of the upstream floodplain on the migratory fish that periodically use the reservoir as feeding habitat. In the tributaries, the temporal changes were less predictable. A combination of habitat preferences and interactions among species, especially predator-prey relations, might be responsible for the observed structure patterns.

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

“…Areas influenced by tributaries have more organic matter and suspended solids, providing temporary habitat for migratory species that use reservoirs as feeding areas (Pagioro and Thomaz, 2002;Oliveira et al, 2005;Miranda and Bettoli, 2010). That may explain the greater abundance of long-distance migratory individuals in the São Simão riverine zone.…”

“…Freshwater fish species respond differently to these riverine/lacustrine zones because the differing habitat types control the spatial distribution of fish species and the resulting fish assemblages (Holmgren and Appelberg, 2000;Irz et al, 2002;Terra et al, 2010). For example, riverine zones tend to support more native species (Oliveira et al, 2005;Agostinho et al, 2007;Gao et al, 2010) and rare species (Oliveira et al, 2003), whereas lacustrine zones tend to support fewer species (Oliveira et al 2004;Agostinho et al, 2007). If reservoir riverine and lacustrine zones support markedly different fish assemblages, it would be wise to manage them differently if managers desire to conserve or rehabilitate native fish assemblages and control invasive non-native species.…”

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

“…Gido et al 2000;Oliveira et al 2005). In the TGR, some exotic species (for example, Ameiurus melas, Tinca tinca, and Ictalurus punctatus) also had successfully colonized the lacustrine zone according to Gao et al (2010).…”

“…Habitats in reservoirs vary longitudinally, allowing the division of three distinct zones: riverine, transitional and lacustrine (Thornton et al 1990). 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).…”

Ecological assessment of a southeastern Brazil reservoir

“…Silva et al (2006) related low correlations between fish abundance and limnological characteristics to a low susceptibility of fish to alterations in limnological characteristics. In contrast, several studies observed associations between abiotic variables and the distribution of the ichthyofauna in this type of environment (Oliveira et al 2005, Prchalová et al 2008. Some environmental variables are particularly associated with fish assemblages, such as depth (Prchalová et al 2008), availability of littoral zone food and shelter (Vidotto & Carvalho 2007), presence of aquatic vegetation (Pelicice et al 2005, Abes & Agostinho 2001, dissolved oxygen, temperature, pH, (Castro et al 2003, Araú jo et al 2009), transparency (Petry et al 2003) and conductivity (Rodríguez & Lewis 1997).…”