Genetic structure and diversity of migratory freshwater fish in a fragmented Neotropical river system

Abstract

Over the past few decades, South American Rivers, including the Paraná River system, have been intensely impacted by dam constructions. To mitigate adverse impacts, fish passages were incorporated into two large dams on the Paraná River (Itaipu and Porto Primavera) to reestablish longitudinal connectivity, which is very important for conserving populations of migratory fish species. The aim of this study was to estimate genetic diversity, population differentiation and gene flow, using microsatellites markers and mitochondrial haplotypes (D-loop), in populations of Prochilodus lineatus, a long distance migratory species commonly found in Paraná River basin drainages. Samples were obtained from six locations in the Upper and Middle Paraná River: Porto Primavera Reservoir, downstream of the Porto Primavera Reservoir, four tributaries of this reservoir (Pardo, Peixe, Verde and Aguapeí Rivers) and in the Iguaçu River, downstream of the Itaipu dam. High genetic diversity was observed in all samples, as expected for species with large population sizes and high migration rates. However, the influence of other factors, such as secondary contacts, fish passages and restocking were also suggested. In general, evidence of spatial population structuring was not found, even though there were two large dams in the study area. This could also be attributed to the brief period that has elapsed since the dams were built, the influence of migratory and reproductive patterns and the possible contributory effects of the fish passages. Furthermore, the absence of population structuring also corroborates existing information that emphasizes the importance of unimpeded tributaries for conserving migratory fish populations in fragmented watersheds.

Bidirectional connectivity via fish ladders in a large Neotropical river

“…The downstream migration in the reproductive period indicated that P. lineatus used different habitats throughout its lifecycle, alternating between upstream and downstream, perhaps as an adaptation strategy to avoid creating subpopulations and genetic structuring (Ferreira et al, ). The descending movements allowed the return of P. lineatus from the breeding areas upstream (Da Silva et al, ) to stretches favourable for feeding downstream of Porto Primavera Dam (Reynalte‐Tataje et al, ).…”

“…These migrations may also contribute to the gene flow between upstream and downstream populations. Ferreira et al () reported high genetic diversity in the P. lineatus population in the Upper Paraná River, which suggested gene flow between the Aguapeí River (tributary of the Porto Primavera Reservoir) and the Iguaçu River (tributary of the Paraná River downstream of the Itaipu Dam). The fishways at Itaipu and Porto Primavera dams most likely facilitate maintaining this gene flow (Ferreira et al, ).…”

“…Observed return cumulative probabilities to the ladder from downstream (0.38, 0.50, and 0.56 in 1–3 years, respectively) reflect return rates mostly from feeding areas in the extensive floodplain between Porto Primavera Dam and the headwaters of the Itaipu Reservoir downstream (approximately a 225‐km stretch, 20‐km wide). Some fish may travel further downstream past Itaipu Dam (Ferreira et al, ). Conversely, return probabilities from upstream (0.15, 0.22, and 0.26) were about 50% lower.…”

“…Thus, as hydropower development is already installed, the challenge is identifying management strategies that minimize the effects of dams on migratory fish species. Proposals include setting aside 100–300 km of protected river stretches with natural flows (Da Silva et al, ; Ferreira et al, ; Pompeu, ), as well as unimpounded tributaries (Da Silva, Miranda, Makrakis, Assumpção, Dias, & Makrakis, accepted for publication; Marques, Dias, Perbiche‐Neves, Kashiwaqui, & Ramos, ). We concur that protecting unimpounded stretches and unimpounded or lightly‐impounded tributaries are important components of an environmental management package.…”

Genetic Applications in the Conservation of Neotropical Freshwater Fish

“…Several studies carried out in the Paraná River Basin have already demonstrated a decline and genetic homogenisation among fish populations in this basin [185][186][187][188]. These studies indicate that the fragmentation of the basin due to the large hydroelectric dams installed in the Paraná River Basin, mainly in the Upper Paraná region, is one of the major factors affecting these populations.…”