Passage of fish larvae and eggs through the Funil, Itutinga and Camargos Reservoirs on the upper Rio Grande (Minas Gerais, Brazil)

Abstract

The objective of this study was to evaluate the passage of fish eggs and larvae through the Funil, Itutinga and Camargos Reservoirs, located in the upper Rio Grande basin, Minas Gerais, Brazil. Samples were taken downstream and upstream of the dams using a conical ichthyoplankton net and were collected every two weeks, twice per sampling day, between November 2008 and March 2009. Although eggs and larvae were abundant immediately upstream of the reservoirs, no ichthyoplankton were captured immediately downstream of the dams, possibly indicating that eggs and larvae do not pass through the reservoirs. The arrival of ichthyoplankton in the reservoirs without its effective passage downstream makes the survival of these eggs and larvae unlikely. Furthermore, this lack of downstream movement may compromise the recruitment of species to downstream stretches, especially in the case of the Funil Reservoir (because of the presence of a fish pass in this dam). We emphasize that the fish lift operation at the Funil Dam must be carefully assessed, considering not only its efficiency but also its short-and long-term effects on the recruitment of migratory fish species from the river.O presente trabalho teve por objetivo avaliar a passagem de ovos e larvas através dos reservatórios de Funil, Itutinga e Camargos, localizados na bacia do alto rio Grande, Minas Gerais, Brasil. As amostragens foram realizadas a jusante e a montante das barragens com auxílio da rede de ictioplâncton cônica. Estas foram conduzidas quinzenalmente, duas vezes ao dia, entre novembro de 2008 e março de 2009. Apesar da elevada abundância de ovos e larvas imediatamente a montante dos reservatórios, não houve capturas de ictioplâncton imediatamente a jusante das barragens, indicando possivelmente a ausência de passagem de ovos e larvas pelos reservatórios do presente estudo. A chegada do ictioplâncton nos reservatórios sem a sua passagem efetiva à jusante torna sua sobrevivência pouco provável. Além disso, a falta desse movimento descendente pode comprometer o recrutamento das espécies aos trechos a jusante, especialmente no caso de Funil, em função da presença do mecanismo de transposição de peixes nessa barragem. Salientamos que a operação do elevador para peixes da barragem de Funil deve ser avaliada com cautela, considerando não apenas sua eficiência, mas também os efeitos a curto e longo prazo no recrutamento das espécies de peixes migradores do rio.

Deficient downstream passage through fish ladders: the case of Peixe Angical Dam, Tocantins River, Brazil

“…At Lajeado Dam, fish migrating downstream were virtually absent from the ladder (Agostinho et al, 2011), and the abundance of eggs and larvae declined dramatically along the reservoir (Agostinho et al, 2007b). The similar trends observed at Peixe Angical and Lajeado, together with other evaluations (Agostinho et al, 2007b;Lopes et al, 2007;Suzuki et al, 2011), indicate that large Neotropical dams may fail to allow the downstream passage of young and adults.…”

“…For example, young (larvae and eggs) do not drift toward downstream areas, probably because they sink in the reservoir (Agostinho et al, 2007b;Suzuki et al, 2011). In addition, the only study that rigorously evaluated the downstream passage of adult fish (Agostinho et al, 2011) revealed that downstream movements through the ladder at Lajeado Dam, Tocantins River, are virtually absent despite the large number of ascending fish recorded over the year.…”

Mapping the Critical Habitats for Migratory Species of the Upper Grande River Region, Minas Gerais State, Brazil

“…The results of this study add the presence of initial developmental sites (floodplain lakes) in the lotic stretches upstream of the reservoir, primarily in the tributaries (Mortes and Capivari). Although the presence of the fish lift is important for maintaining connectivity between habitats, the functioning of this fish passage should be studied and carefully monitored because there is no descending ichthyoplankton migration downstream (Suzuki et al, 2011). The absence of this migration makes the Funil fish lift one way, which could compromise fish species recruitment downstream of the dam (Suzuki et al, 2011) and consequently undermine its value in conserving the basin's fish species .…”

“…Although the presence of the fish lift is important for maintaining connectivity between habitats, the functioning of this fish passage should be studied and carefully monitored because there is no descending ichthyoplankton migration downstream (Suzuki et al, 2011). The absence of this migration makes the Funil fish lift one way, which could compromise fish species recruitment downstream of the dam (Suzuki et al, 2011) and consequently undermine its value in conserving the basin's fish species . Its function should be primarily aimed at maintaining genetic flow between populations, where in principle, the populations upstream and downstream would be self-sustaining due to the occurrence of spawning and nurseries areas.…”

“…The presence of these dams may be a critical factor in the success of fish recruitment in this basin. The reservoirs act as obstacles to ichthyoplankton from the lotic remnants of the basin (Suzuki et al, 2011). Among the hydroelectric dams mentioned, only the Funil Dam incorporates a fish passage mechanism (fish lift) in which many fish are transported upstream during the spawning season (Suzuki et al, 2011).…”