Downstream passage of fish larvae and eggs through a small-sized reservoir, Mucuri river, Brazil

Abstract

In South America, one important symptom of the failure of fish passages to sustain fish migratory recruitment is the inability of eggs and larvae to reach the nurseries. This is especially so when the breeding areas are located upstream of a reservoir, and the floodplain is downstream of the dam. Therefore, the transport of fish larvae and eggs across reservoir barriers is a key factor in the development of effective conservation strategies. In this paper, we evaluate the potential for migratory fish larvae and egg transportation across a small size reservoir in eastern Brazil. We sampled fish daily between 15th October 2002 and 15th February 2003 (spawning period) in the Mucuri River, immediately upstream of the reservoir and downstream of the Santa Clara Power Plant dam. Our study was the first to indicate the possibility of successful larval passage through the reservoir of a hydroelectric reservoir and dam in South America, and showed that the passage of migratory fish larvae was associated significantly with residence time of water in the reservoir. The relatively short water residence time and elevated turbidity of the Santa Clara's reservoir waters during the rainy season certainly contributed to the successful passage, and can be considered as key factors for a priori evaluations of the feasibility of a downstream larval passage

Downstream Passage of Fish Larvae at the Salto Grande Dam on the Uruguay River

“…The results are coherent with the low percentage of injuries (<10%) in fish larvae captured by Pompeu et al . (), and the low mortality (<5%) predicted for preflexion larvae and the same type of turbines (Cada, ). Additionally, the body of the preserved larvae captured downstream of the dam (HFIM and Surveys 1–5), regardless of the flow rate, showed characteristics of ‘live’ individuals (curvy and not damaged), which suggests that both turbine and spillway passage would likely be endured by the larvae.…”

“…Interestingly, we found that passage is possible even for a reservoir of considerable size, such as that produced by the Salt Grande Dam (783 km 2 ). The low water residence time (<10 days), which is similar to or even lower than that described for the Santa Clara Dam (Pompeu et al ., ), and the high water turbidity of the reservoir during high flow conditions could perhaps contribute, in part, to the downstream passage of the larvae through the Salto Grande Dam. The low number of impoundments in the middle Uruguay River contrasts with the heavy damming of the upper section of the Paraná River, which impaired or heavily reduced both the upriver movements by adults and the downstream distribution of early developmental stages (Agostinho et al ., ; Suzuki et al ., ; Pelicice et al ., ).…”

Large reservoirs as ecological barriers to downstream movements of Neotropical migratory fish

“…Even in small reservoirs, the downstream passage of eggs and larvae seems to be limited and dependent on variations in water residence, and this was demonstrated in the Santa Clara Dam, a short and small reservoir of 7.5 km 2 surface area (Pompeu et al . ). Based on this evidence, the reservoir seems to interrupt the downstream drift of ichthyoplankton towards lower reaches.…”

“…) and Santa Clara (Pompeu et al . ). Note that area, length and water residence of these reservoirs are far below the average observed across all Brazilian basins (Fig.…”

“…Relationship between length (km, log) and water residence time (days, log) of the reservoirs analysed in this study, indicating the minimum reservoir dimension (length × residence) in which the downstream passage of eggs and larvae was recorded (Santa Clara Dam; Pompeu et al . ) and prevented (Funil Dam; Suzuki et al . ).…”