Fish passages in South America: an overview of studied facilities and research effort

Abstract

River regulation has fragmented fluvial ecosystems in South America, affecting fish migration and dispersion dynamics. In response, authorities have installed fish passage facilities (FPF) to mitigate impacts. However, little is known about the geographical distribution of these facilities, and no synthesis of the research effort applied to understanding their functioning and limitations exists. To address this issue, our study gathered the available scientific literature about fishways in South America to provide an overview of studied FPF and associated research effort. We found 80 studies that investigated 25 FPF, mostly ladders installed in the upper reaches of large rivers, particularly in the Paraná River Basin. One important finding is that most facilities do not lead to upstream and/or downstream sites due to the presence of other dams with no FPF. Though the number of studies has increased over the past 10 years, there is no consistent trend towards increased research effort. Overall, studies have focused on the fishway itself (i.e. upstream passage), and rarely evaluated broader issues (i.e. habitat distribution, population dynamics, conservation and management success). Our research therefore identified technical limitations of past studies, and revealed important gaps in the knowledge of FPF as a management tool.Keywords: Conservation, Dam, Fishway, Impact, Management.A implantação de barragens tem perturbado e fragmentado os ecossistemas fluviais da América do Sul, afetando a migração dos peixes e dinâmicas de dispersão. Sistemas de transposição de peixes (STPs) têm sido instalados na tentativa de atenuar esses impactos. No entanto, pouco se sabe sobre a distribuição geográfica desses dispositivos, bem como o esforço de pesquisa aplicado para entender seu funcionamento e limitações. Nosso trabalho reuniu a literatura disponível com a finalidade de fornecer um panorama sobre os mecanismos investigados na América do Sul, bem como revelar o esforço e perfil das pesquisas. Encontramos 80 estudos que investigaram 25 STPs, a maioria escadas instaladas nos trechos superiores de grandes rios, particularmente na bacia do rio Paraná. Um resultado interessante é que a maior parte dos STPs está desconectada de trechos a montante e jusante devido à presença de outras barragens sem STPs. Embora o número de estudos tenha aumentado na última década, não registramos tendência consistente de incremento ao longo dos anos. No geral, os estudos abordam aspectos do próprio STP, especificamente a passagem ascendente, ignorando temas mais abrangentes (i.e. distribuição de habitats, dinâmica populacional). Além disso, o foco da pesquisa se direciona especialmente às questões de eficiência da passagem e raramente ao contexto da conservação e sucesso do manejo. Nossa avaliação, portanto, indicou que os estudos pretéritos são tecnicamente limitados, revelando importantes lacunas sobre o conhecimento dos STPs como medida de manejo.

The critical importance of an undammed river segment to the reproductive cycle of a migratory Neotropical fish

“…ity parameters and reduced connectivity of habitats within basins (Agostinho, Gomes, Santos, Ortega, & Pelicice, 2016;Lira et al, 2017). These rapid alterations cause population declines, and many migratory species are threatened with extinction in the continent (Barletta et al, 2010;Pelicice et al, 2017;Reis et al, 2016).…”

Moving beyond fitting fish into equations: Progressing the fish passage debate in the Anthropocene

“…Despite the significant differences between the requirements of salmonids and most other fishes (Figure ), including those from the tropics and temperate Southern Hemisphere, the knowledge, techniques, thinking and solutions developed from studies of salmonids have been widely transferred to fish passage design and management elsewhere (Silva et al, ). Application of these approaches to freshwater systems with native species that have completely different needs has contributed to repeated failures and poor performance of fishways around the world (Lira et al, ; Wilkes, McKenzie et al, ). For example, Mallen‐Cooper and Brand () showed very poor passage of native Australian fish species through a salmonid fishway on the Murray River, with <1% of the most abundant species ascending.…”

“…There is strong evidence that removing artificial barriers to migration can be cost‐effective and result in the rapid recovery of freshwater biodiversity and ecosystem processes, as seen for American eel ( Anguilla rostrata ; Hitt, Eyler, & Wofford, ), sea lamprey ( Petromyzon marinus ; Hogg, Coghlan, & Zydlewski, ) and brown trout ( Salmo trutta ; Birnie‐Gauvin, Larsen, Nielsen, & Aarestrup, ; Birnie‐Gauvin et al, in press), as well as other species (O'Connor, Duda, & Grant, ), yet barrier removal remains relatively uncommon, even where structures are redundant. Consequently, despite the growing use of fishways, which are supposedly designed to allow migrating fish to bypass barriers and reach suitable habitat in which to grow and reproduce, these structures remain mere pacifiers of the underlying ecological problems (Bunt et al, , ; Lira et al, ; Noonan et al, ; Roscoe & Hinch, ).…”

“…. Application of these approaches to freshwater systems with native species that have completely different needs has contributed to repeated failures and poor performance of fishways around the world (Lira et al, 2017;Wilkes, McKenzie et al, 2018). For example, Mallen-Cooper and Brand (2007) showed very poor passage of native Australian fish species through a salmonid fishway on the Murray River, with <1% of the most abundant species ascending.…”

Reproductive cycle of the Amazonian planktivorous catfish Hypophthalmus marginatus (Siluriformes, Pimelodidae)

“…Posteriorly, the upstream region of the dam has also been included as a spawning area during the flood period from October to March (Cintra et al, 2007). However, as described for other migratory species (Honji, Narcizo, Borella, Romagosa, & Moreira, 2009;Lira et al, 2017;Makrakis, Gomes, Makrakis, Fernandez, & Pavanelli, 2007;Mérona, Juras, Santos, & Cintra, 2010), it is possible that spawning of this species in the dam region has been altered, although nothing is known regarding this concern.…”