Is there evidence of connectivity restoration by fishways? The case of Porto Primavera Hydropower Plant, Paraná River, Southeastern Brazil

Hugo Marques, João Henrique Pinheiro Dias, Igor Paiva Ramos

Resumo


Habitat fragmentation is one of the main impacts of river damming and fishways could be an important management tool to mitigate it, restoring river connectivity. The Porto Primavera dam is located in the upper Paraná River basin, Southeast Brazil, built on an alluvial floodplain with important tributaries serving as nursery sites both upstream and downstream. Its reservoir was filled in December/1998 and the pool‐weir‐orifice fishway was opened in October/2001. We test the hypothesis that the fishway increases the river connectivity using beta diversity as an indicator, once lower values of this metrics indicate higher similarity among fish assemblages. Quarterly sampling with gillnets was performed upstream and downstream of the dam before fishway opening, from February/1999 to May/2001 and from February 2003 to May/2005, with fishway operating (10 samples per period/site). The numeric abundance data was indexed by catch per unit effort (number of individuals per 1000 m² gillnet, set for 24 h). First, we verify the correlation of fish assemblages between sites applying two Mantel tests (downstream versus upstream before and one equivalent after the fishway) using the distance matrices generated by the Bray‐Curtis index. Then we calculate the beta diversity partitioned using Sorensen index, between downstream and upstream for each sampling to compare the beta diversity values before and after the fishway, by the Asymptotic Wilcoxon‐Mann‐Whitney Test. The mantel tests showed no correlation between the upstream and downstream assemblages before the fishway but correlated after (r=0.322, p=0.03). The beta diversity presented lower values after (median 0.47) than before (median 0.57) (Z=‐2.08, p=0.04), evidencing the increase of similarity between downstream and upstream the dam with the fishway. Although fishways remain an incipient and controversial theme for Neotropical fishes, mainly in demographic and genetic aspects, the Porto Primavera fishway is probably effective for the aspect of connectivity restoration.

Palavras-chave


fish passage; fish assemblage; fluvial connectivity; β diversity; conservation

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