Impact of a hydroelectric power plant on migratory fishes in the Uruguay River

Abstract

Dams alter river functioning and hinders the free movement of migratory fishes. We analysed the effects of a subtropical dam on the reproduction of migratory fishes using data from ichthyoplankton monitoring surveys. These were conducted at six sampling stations upstream, downstream and within the reservoir on a weekly basis during 6 years. The dam had a direct impact on fish movement, leading to the fragmentation of fish populations. Two different and independent reproductive areas became evident: one located in the reservoir headwater area and the other downstream of the dam. The long temporal scale of our study facilitated the detection of the impact of Salto Grande on the species of ichthyoplankton. Freshwater secondary fish species (mainly Lycengraulis grossidens) increased in abundance in the stations located inside the reservoir and closer to the dam, whereas most fishes found in the headwater of the reservoir corresponded to river migratory species (potamodromous fish). These differences are most likely due to changes in the physicochemical characteristics of the water induced by the transformation of a river into a reservoir. During rainy summers, Microcystis spp. densities were lower than 1,000 cells ml −1 and fish densities were higher than 4 ind. m −3 , whereas in dry summers, there were important Microcystis spp. blooms (401,573 ± 112,559 cells ml −1) and fish larvae decreased sharply (<1 ind. m −3) in the reservoir headwater area. This could indicate that the discharge of water in the reservoir may also indirectly affect the regulation of fish reproduction. The alternating periods between dry and rainy summers associated with El Niño-Southern Oscillation poses a challenge to ichthyofauna management in the reservoir.

Altitudinal distribution and body condition of migratory fish juveniles Megaleporinus obtusidens (Valenciennes) and Salminus brasiliensis (Cuvier) in the main channel of the Uruguay River, Southern Brazil

“…Finally, the Uruguay River has a cascade effect in its upper part caused by 3 dams already built (Machadinho, Itá, and Foz do Chapecó). Furthermore, approximately 300 km below the last sampling point, the Uruguay River is dammed by the Salto Grande hydroelectric power plant, which has a severe negative impact on the recruitment of migratory fish populations in the Uruguay River (Cataldo et al, 2020). Therefore, future economic development plans that could compromise the environmental functions of the free stretch of the middle portion of the Uruguay River, such as hydroelectric dams, should consider the pivotal ecological roles of nurseries for migratory fish, particularly the T3 region and, the also fundamental ecological role of T1 and T2 as possible fish spawning areas (Mounic-Silva et al, 2019).…”

“…These species are targets of commercial and sport fishing in the Uruguay River (Schork et al, 2012), and face considerable fishing pressure in the Uruguay River Basin, with the dourado assigned a vulnerable status on the Red List of Endangered Species for the Rio Grande do Sul state (Marques et al, 2002). They also face other environmental pressures in this river basin, such as habitat degradation; interruption of migratory routes (upstream and downstream) by hydroelectric dams; and heavy pollution from agricultural, livestock, urban, and industrial activities (Reynalte-Tataje et al, 2012;Lopes and Zaniboni-Filho, 2019;Cataldo et al, 2020).…”

Global trends, biases and gaps in the scientific literature about freshwater fish eggs and larvae

“…They selected variables related to infrastructure development and socio‐economic factors (variables: i to iv) because the variables are proxy for scientific production of each country (Hughes et al ., 2021; Oliveira et al ., 2016). Hydrological variables (v to vii) and the use of aquatic resources (viii and ix) were chosen because they are associated with the conduction of monitoring and impact assessments (Cataldo et al ., 2020; Kelso & Milburn, 1979; Song et al ., 2019). Variables (i) to (vii) were extracted from the HydroATLAS database (Linke et al ., 2019) and expressed as mean values for each ecoregion.…”

Efecto de la bajante extrema 2020-2023 sobre la reproducción de peces migradores en el río Uruguay

“…Las variaciones de la altura del agua en los ríos de la CP ejercen un fuerte efecto sobre las características físicas y químicas del agua, tales como la concentración de nutrientes, la transparencia del agua, el pH, el oxígeno disuelto y el carbono orgánico particulado (Villa y Bonetto, 2000). También influyen sobre las comunidades biológicas como, por ejemplo, la abundancia y composición del fitoplancton (O'Farrell et al, 2012), el zooplancton (Boltovskoy et al, 2021) y la ictofauna (Cataldo et al, 2020); o sobre la ocurrencia de floraciones de cianobacterias (O'Farrell et al, 2012;Kruk et al, 2023;Ferrari, 2020).…”

“…Durante épocas de sequía han sido reportados efectos negativos en la reproducción de peces en general y migradores en particular en los ríos Pilcomayo (Smolders et al,2000), Paraná superior (Alves et al, 2021), Amazonas (Camacho Guerreiro et al, 2021;Fabré et al, 2017) y Uruguay (Cataldo et al, 2020). Las características de la CP también son afectadas por otros factores no atmosféricos, como el uso del suelo (Saurral et al, 2008) y aportes de residuos domiciliarios de las poblaciones humanas localizadas en sus márgenes sin un adecuado tratamiento.…”