Upstream and downstream responses of fish assemblages to an eastern Amazonian hydroelectric dam

Abstract

Major hydroelectric dams are proliferating in tropical regions such as Amazonia, where extensive new hydropower developments are planned despite potentially severe ecological and social impacts. The status of freshwater biota in the vicinity of existing dams could be valuable to predict the effects of such developments, but detailed ecological monitoring before and after dam construction is frequently lacking. In the absence of these data, we used a space-for-time replacement to compare a key component of the aquatic biota at upstream and downstream sites, with the latter more closely resembling river channel conditions prior to the dam. We assessed the fish assemblages upstream and downstream of the Coaracy Nunes Dam in Amapá, Brazil, the first ecological study at this site since this dam was constructed 42 years earlier. We used gillnets during eight bimonthly field campaigns, covering both wet and dry seasons, and sampled the ichthyofauna (1819 individuals, 81 species) at four sites: Downstream Channel, Reservoir, Upstream Lake and Upstream Channel. We found clear negative impacts on the abundance, biomass, species richness, alpha diversity and species dominance upstream of the dam. The physical subdivision of the river channel and the upstream channel conversion from lentic to lotic habitats were strongly associated with differences in the composition and structure of fish communities. Notable changes include an increased contribution of small-bodied fish in the reservoir and an absence of long-distance migrants upstream of the dam. Downstream channel habitats, in particular, retained their fish diversity with high conservation value typical of eastern Amazonia, yet these areas now face the threat of new hydropower development farther downstream. The long-term impacts on aquatic biodiversity highlighted in this study are especially relevant in the face of burgeoning new hydroelectricity development plans for rivers across lowland Amazonia

Temporal fish community responses to two cascade run‐of‐river dams in the Madeira River, Amazon basin

“…The present study confirmed the occurrence of early and significant changes in some fish assemblage attributes, as expected for the heterotrophic phase of accumulation reservoirs. Reductions in species richness and fish diversity still can be expected after the heterotrophic phase of the reservoir (Agostinho et al, ; Sá‐Oliveira et al, ), but they are usually detected a few years after dams closure in accumulation reservoirs (Lima et al, ; Lima et al, ). Compared to vertical models, horizontal bulb turbines work with slower water velocity, which results in fish experiencing a more prolonged, albeit less severe, pressure change (Pracheil et al, ).…”

“…These man‐made reservoirs modify limnological characteristics and can trigger changes in fish assemblage structure and composition, favouring the replacement of reophilic fish assemblages by a set of predominantly sedentary fish species (Agostinho, Gomes, Santos, Ortega, & Pelicice, ; Agostinho, Pelicice, & Gomes, ; Poff, Olden, Merritt, & Pepin, ). The construction of large reservoirs in large rivers causes rapid and drastic changes in the environment, promoting almost immediate responses in fish populations (Agostinho et al, ; Gehrke, Gilligan, & Barwick, ; Lima, Agostinho, Soares, & Monaghan, ; Lima et al, ; Sá‐Oliveira, Hawes, Isaac‐Nahum, & Peres, ). In addition, dams are recognized by fragmenting lotic habitats and preventing most fish migrations because the reservoirs may act as ecological traps for migratory fish species even when a transposition system (fish passage) is present (Agostinho, Agostinho, Pelicice, & Marques, ; Pelicice & Agostinho, ).…”

Predictors of specialist avifaunal decline in coastal marshes

“…) and biodiversity (Sá‐Oliveira et al. ), and the recent removal of 2 large dams in northwestern North America demonstrates the large‐scale return of sediment to riverine and coastal systems (East et al. ; Gelfenbaum et al.…”

Dams have varying impacts on fish communities across latitudes: a quantitative synthesis

“…the process by which ecosystems lose their biological uniqueness; Rahel 2000;Poff et al 2007;Gido et al 2009;Vill eger et al 2011;Liermann et al 2012;Vitule et al 2012). At a more local scale, empirical evidence shows that richness and diversity decreases after impoundment, or is lower in reservoirs (Reyes-Gavil an et al 1996;Pyron et al 1998;Gehrke et al 2002;de M erona et al 2005;S a-Oliveira et al 2015;Lima et al 2016a). Conversely, other studies and a recent meta-analysis (Liew et al 2016) found either no change or an increase in richness and diversity after impoundment in reservoirs (Martinez et al 1994;Guenther & Spacie 2006;Irz et al 2006).…”