Efeito dos barramentos de pequenas centrais hidrelétricas sobre a distribuição do ictioplâncton em um tributário do Rio Grande (SP/MG)
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Data
2020-02-28
Autores
Brambilla, Eduardo Meneguzzi
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Universidade Estadual Paulista (Unesp)
Resumo
Uma das melhores alternativas para minimizar os impactos de barramentos na ictiofauna de grandes rios é a conservação de seus tributários, que servem como rotas alternativas para migração reprodutiva e disponibilizam novos habitats necessários para desova e crescimento. Porém, devido a alta demanda de energia elétrica no país muitos destes tributários estão sendo barrados por Pequenas Centrais Hidrelétricas (PCHs). Nesse contexto se destaca o rio Sapucaí-Mirim, um dos principais tributários do rio Grande. Uma importante ferramenta para avaliar o real impacto destes empreendimentos na reprodução e recrutamento de peixes é o estudo de ictioplâncton. Portanto, o objetivo geral deste trabalho foi avaliar os processos reprodutivos da ictiofauna, através da análise de ovos e larvas de peixe, em dois reservatórios de PCHs do rio Sapucaí-Mirim. As amostragens foram realizadas quinzenalmente, nos ciclos reprodutivos de novembro de 2015 a fevereiro de 2016 e novembro de 2016 a fevereiro de 2017 em oito pontos amostrais incluindo os trechos lótico, transição, lêntico e dentro da escada de peixes de cada um dos reservatórios. No total foram amostrados 5.004 ovos e 3.189 larvas de 22 táxons pertencentes a quatro ordens e 15 famílias. As famílias mais abundantes foram Anostomidae, Characidae, Pimelodidae e Prochilodontidae, com predominância de ovos e larvas de desenvolvimento inicial (larval vitelino e pré-flexão). A estrutura da assembléia de larvas de peixes e estágios de desenvolvimento, em ambos os ciclos reprodutivos, foram influenciados por fatores espaciais e temporais. Temporalmente, maiores densidades de ovos e larvas foram observadas em períodos com alta pluviosidade e alterações associadas nas variáveis ambientais. Espacialmente, maiores densidades de ovos foram encontradas no reservatório mais a montante e as densidades de larvas variaram de acordo com o ciclo reprodutivo. Os trechos com maiores densidades de ovos foram lóticos em 2015-2016 e transição em 2016-2017 e para larvas foi transição em ambos os ciclos. Houve dispersão descendente de ovos e larvas ao longo do trecho estudado sendo influenciada por uma combinação de variação de chuva/vazão do rio e período do ciclo reprodutivo com pico de chuva durante o verão coincidindo com maiores abundâncias. Sob essas condições, ovos e larvas derivaram rio abaixo através dos reservatórios e atingiram as barragens. Uma vez na barragem, os individuos puderam passar pela escada de peixes e foram correlacionados com a densidade no reservatório imediatamente a montante, embora em densidades muito baixas em comparação com os outros locais de amostragem. Houve também uma influência de eventos climáticos extremos na reprodução dos peixes, com um período de chuvas extremas apresentando 10 vezes mais ovos e larvas e maior proporção de espécies migradoras do que um período de seca extrema. Densidades de ovos e larvas foram correlacionadas positivamente com turbidez e vazão e negativamente com temperatura, sólidos totais em suspensão, condutividade e pH. Em conclusão, este trecho do rio Sapucaí-Mirim oferece condições adequadas para desova e deriva de ovos e larvas de importantes espécies migratórias da bacia hidrográfica. Portanto, esta é uma área crítica para o recrutamento de peixes e são necessários esforços para preservá-lo.
One of the best alternatives to minimize the impacts of dams on the ichthyofauna of large rivers is the conservation of their tributaries, which serve as alternative routes for reproductive migration and provide new habitats necessary for spawning and growth. However, due to the high demand for electricity in the country, many of these tributaries are being dammed by small hydropower plants (SHPs). In this context highlights the Sapucaí-Mirim River, one of the main tributaries of the Grande River. An important tool to assess the real impact of these enterprises on the reproduction and recruitment of fish is the study of ichthyoplankton. Therefore, the general aim of this work was to evaluate the reproductive processes of the ichthyofauna, through the analysis of fish eggs and larvae, in two reservoirs of SHPs on the Sapucaí-Mirim River. Sampling was carried out fortnightly, in the reproductive cycles from November 2015 to February 2016 and November 2016 to February 2017 at eight sample points including the lotic, transition, lentic and within the fish ladder sections of each reservoir. In total, 5,004 eggs and 3,189 larvae from 22 taxa belonging to four orders and 15 families were sampled. The most abundant families were Anostomidae, Characidae, Pimelodidae and Prochilodontidae, with a predominance of eggs and larvae of initial development (yolk-sac and preflexion). The larval assemblage structure and early development stages, in both reproductive cycles, were influenced by spatial and temporal factors. Temporally, higher densities of eggs and larvae were observed in periods with high rainfall and associated changes in environmental variables. Spatially, higher egg densities were found in the reservoir more upstream and the larvae densities varied according to the reproductive cycle. The sections with the highest egg densities were lotic in 2015-2016 and transition in 2016-2017 and for larvae was transition in both cycles. There was a downstream dispersion of eggs and larvae along the studied section, being influenced by a combination of variation of rain / river outflow and period of the reproductive cycle with peak of rain during the summer coinciding with higher abundances. Under these conditions, eggs and larvae drifted downstream through the reservoirs and reach the dams. Once at the dam, individuals were able to pass the fish ladder and were correlated with the density in the reservoir immediately upstream, although at very low densities compared to the other sampling sites. There was also an influence of extreme climatic events on fish reproduction, with a period of extreme rain presenting 10 times more eggs and larvae and a greater proportion of migratory species than a period of extreme drought. Densities of eggs and larvae were positively correlated with turbidity and outflow and negatively correlated with temperature, total suspended solids, conductivity and pH. In conclusion, this stretch of the Sapucaí-Mirim River offers adequate conditions for spawning and drift of eggs and larvae of important migratory species from the hydrographic basin. Therefore, this is a critical area for recruiting fish and efforts are needed to preserve it.
One of the best alternatives to minimize the impacts of dams on the ichthyofauna of large rivers is the conservation of their tributaries, which serve as alternative routes for reproductive migration and provide new habitats necessary for spawning and growth. However, due to the high demand for electricity in the country, many of these tributaries are being dammed by small hydropower plants (SHPs). In this context highlights the Sapucaí-Mirim River, one of the main tributaries of the Grande River. An important tool to assess the real impact of these enterprises on the reproduction and recruitment of fish is the study of ichthyoplankton. Therefore, the general aim of this work was to evaluate the reproductive processes of the ichthyofauna, through the analysis of fish eggs and larvae, in two reservoirs of SHPs on the Sapucaí-Mirim River. Sampling was carried out fortnightly, in the reproductive cycles from November 2015 to February 2016 and November 2016 to February 2017 at eight sample points including the lotic, transition, lentic and within the fish ladder sections of each reservoir. In total, 5,004 eggs and 3,189 larvae from 22 taxa belonging to four orders and 15 families were sampled. The most abundant families were Anostomidae, Characidae, Pimelodidae and Prochilodontidae, with a predominance of eggs and larvae of initial development (yolk-sac and preflexion). The larval assemblage structure and early development stages, in both reproductive cycles, were influenced by spatial and temporal factors. Temporally, higher densities of eggs and larvae were observed in periods with high rainfall and associated changes in environmental variables. Spatially, higher egg densities were found in the reservoir more upstream and the larvae densities varied according to the reproductive cycle. The sections with the highest egg densities were lotic in 2015-2016 and transition in 2016-2017 and for larvae was transition in both cycles. There was a downstream dispersion of eggs and larvae along the studied section, being influenced by a combination of variation of rain / river outflow and period of the reproductive cycle with peak of rain during the summer coinciding with higher abundances. Under these conditions, eggs and larvae drifted downstream through the reservoirs and reach the dams. Once at the dam, individuals were able to pass the fish ladder and were correlated with the density in the reservoir immediately upstream, although at very low densities compared to the other sampling sites. There was also an influence of extreme climatic events on fish reproduction, with a period of extreme rain presenting 10 times more eggs and larvae and a greater proportion of migratory species than a period of extreme drought. Densities of eggs and larvae were positively correlated with turbidity and outflow and negatively correlated with temperature, total suspended solids, conductivity and pH. In conclusion, this stretch of the Sapucaí-Mirim River offers adequate conditions for spawning and drift of eggs and larvae of important migratory species from the hydrographic basin. Therefore, this is a critical area for recruiting fish and efforts are needed to preserve it.
Descrição
Palavras-chave
Biodiversidade, Conservação, Ictiofauna, Rio Sapucaí-Mirim, Ovos e larvas de peixe