Dispersal of fish eggs and larvae in a cascade of small hydropower plants with fish ladders

Abstract

This study was conducted to investigate fish eggs and larvae dispersal in a river stretch influenced by small hydropower plants in Southeast Brazil. The main hypothesis is that the downstream dispersal of free-flowing eggs and larvae is likely to occur given the small size of the studied reservoirs and that passage through the dam may occur, with the fish ladder contributing to it. Eggs and larvae were collected fortnightly, between November 2016 and February 2017, from locations upstream of two dams, including lotic, transition and lentic zones. Additional samples were collected inside the fish ladders at each dam. Downstream dispersal of eggs and larvae was influenced by a combination of rainfall/flow variation and stage of the reproductive cycle, with the peak of rainfall during the summer coinciding with higher abundances. Under these conditions, eggs and larvae drifted downstream through the reservoirs and reached the dams. Once in the dam, they could pass through the fish ladder. This passage was correlated with larval density in the reservoir immediately upstream, although at very low densities compared with the other sampling sites located upstream of the fish ladders.

Spatial and seasonal distribution of fish eggs and larvae in one free‐flowing river in the Neotropical savanna

“…On the contrary, the frequency of fish eggs and larvae sampled in the surface sampling may be attributed to the greater presence of pelagic eggs and the turbidity of the sampled rivers. Recent studies have suggested that precipitation and turbidity are the main triggers for spawning, which provide higher densities of fish eggs and larvae under these conditions (Brambilla et al ., 2022; Lopes et al ., 2019; Makrakis et al ., 2022). Furthermore, it is known that the presence of eggs may be the result of past events ( i.e ., 1–3 days earlier; see Nakatani et al ., 2001); consequently, the density of eggs may be attributed to the time from development to hatching and not only to the spawning time.…”

Perspectives on the environmental implications of sustainable hydro-power: comparing countries, problems and approaches

“…One potential issue with the use of fishways as a management tool for Neotropical species is that, by enabling fish to reach spawning grounds upstream of reservoirs (even though suitable spawning grounds may be available downstream of dams), their eggs and larvae may suffer high mortality as they drift downstream through the dam created lentic environment and/or move through turbines or spillway intakes (Pelicice et al, 2015;Boys et al, 2016). Brambilla et al (2021) studied the downstream dispersal of fish eggs and larvae through reservoirs created by small hydropower facilities to determine which factors influence their drift and whether downstream passage through fishways can occur. The authors regularly sampled larvae and eggs from the riverine, transition and lentic zones of two small reservoirs as well as in the fishways associated with the dams forming the reservoirs.…”

“…Considered together, the papers in this issue point to a series of important conclusions regarding the sustainability of hydropower and the ways in which it can be made and maintained as environmentally friendly as possible. Technology and technological change emerging from environmental studies have important roles to play, in the context of providing researchers with new tools to understand the nuances of fish ecology, such as downstream larval dispersal (Brambilla et al, 2021), and fish interactions with hydropower facilities (Hahn et al, 2021). New hydropower engineering technologies will be similarly important for understanding how hydropower operational regimes may be adjusted to account for fish behaviour in ways that will reduce overall mortality (Smokorowski, 2021;Stenberg et al, 2021;Tuononen, et al, 2021).…”

Importance of a turbulent river section below a giant waterfall for fish spawning: Indications from drift and dispersion patterns of early life stages

“…In South American rivers, the first studies on ichthyoplankton transport were carried out in the Solimões and Amazonas rivers (Araujo‐Lima & Oliveira, 1998), and in the Paraná River (Baumgartner et al, 2004; Bialetzki et al, 1999). Currently, studies evaluating fish reproduction behaviour and dynamics have been conducted in several river basins with a focus on assessing the ichthyoplankton drift pattern related to the impact of hydroelectric plants (Barthem et al, 2014; Brambilla et al, 2020; Da Silva et al, 2020; Fuentes et al, 2016; Garcia et al, 2018; Mounic‐Silva et al, 2019; Suzuki et al, 2013). And the free‐flowing rivers, especially dam‐free tributaries, has been an appeal for the conservation of fish species (Da Silva et al, 2015, 2019; Makrakis et al, 2019; Marques et al, 2018; Silva et al, 2017).…”