Spatial and temporal variations in fish assemblage: testing the zonation concept in small reservoirs

Abstract

Large reservoirs usually present spatial gradients in fish assemblage, distinguishing three strata (littoral, pelagic, and bathypelagic) along the vertical and horizontal axes, and three zones (fluvial, transitional, and lacustrine) along the longitudinal axis. The main objective of this study was to assess if small reservoirs also present the spatial gradients in fish assemblage attributes and structure as already observed in large reservoirs. Fish surveys were conducted quarterly, from 2003 to 2008, in the Mourão Reservoir (Mourão River, Paraná, Brazil), using gillnets with different mesh sizes, arranged in all strata of all three zones. Community attributes (species richness and evenness) were calculated for each sample, and differences were tested using three-way ANOVA (factors: zone, strata, year). Community composition was summarized using Correspondence Analysis (CA) and differences were tested with three-way ANOVA for each axis, controlling the same three factors. Because of the high variability in reservoir water level through time, all analyses were made considering temporal variations. Species richness presented a decreasing trend from fluvial to lacustrine zones, and higher values in littoral strata, possibly because upper reaches and littoral regions provide better conditions for fish to feed and to reproduce. Evenness was considerably low, presenting high variability, and no evident pattern. The expected longitudinal gradient was not found in this study indicating longitudinal similarity, contrary to observed in large reservoirs. Vertical and horizontal gradients were observed in all sampling stations, indicating that abiotic and biotic conditions are influencing fish distributions within the reservoir.Keywords: dam, longitudinal gradients, impoundment, gradient. Variações espaciais e temporais na assembleia de peixes: testando o conceito de zonação em pequenos reservatórios ResumoGrandes reservatórios, em geral, apresentam gradientes espaciais da assembleia de peixes, distinguindo três estratos (litoral, pelágico e batipelágico) ao longo dos eixos vertical e horizontal, e três zonas (fluvial, transição e lacustre) ao longo do eixo longitudinal. O principal objetivo deste estudo foi avaliar se pequenos reservatórios também apresentam tais gradientes espaciais, nos atributos e na estrutura da assembleia de peixes, como já observado em grandes reservatórios. As coletas dos peixes foram realizadas trimestralmente, de 2003 a 2008, no reservatório de Mourão (Rio Mourão, Paraná, Brasil), com redes de espera com diferentes tamanhos de malha, dispostas em todos os estratos de todas as três zonas. Atributos da assembleia (riqueza de espécies e equitabilidade) foram calculados para cada amostra, e as diferenças foram testadas utilizando ANOVA tri-fatorial (fatores: zona, estratos, anos). A estrutura da assembleia foi sumarizada usando uma Análise de Correspondência (CA) e as diferenças foram testadas com ANOVA tri-fatorial para cada eixo, controlando os mesmos três fatores. Devido à alta variabilidad...

Damming and seasonality as modulators of fish community structure in a small tributary

“…The effects of compartmentalisation and seasonality have been widely studied in isolation in large dammed rivers, as Paraná and Tocantins Rivers (Agostinho et al, ; Araújo et al, ; Ortega, Dias, Petry, Oliveira, & Agostinho, ), which presents hundred metres of width, hundred kilometres in length and several large tributaries on its course, that presents large dams. However, few studies have investigated damming effects of habitat compartmentalisation in concert with seasonality in smaller tributaries (Baumgartner, Baumgartner, & Gomes, )…”

“…The effects of compartmentalisation and seasonality have been widely studied in isolation in large dammed rivers, as Paraná and Tocantins Rivers Araújo et al, 2013;Ortega, Dias, Petry, Oliveira, & Agostinho, 2015), which presents hundred metres of width, hundred kilometres in length and several large tributaries on its course, that presents large dams. However, few studies have investigated damming effects of habitat compartmentalisation in concert with seasonality in smaller tributaries (Baumgartner, Baumgartner, & Gomes, 2017) Therefore, we tested the hypothesis that longitudinal gradient and seasonality act simultaneously as modulators of fish community structure of a small tributary under influence of a large damming (high retention time). We expected that spatial variation would be more pronounced than temporal variation because damming and the lack of downstream riparian vegetation likely decreases seasonal variability of fluvial habitats .…”

Distribution of Siluriformes in a river under the influence of a small hydroelectric power plant of the Paraná River Basin, Brazil

“…al., 2018). However, studies of small hydroelectric power plants (SHPs) have shown that such small impoundments might present different patterns from those usually observed in large dams (Baumgartner et al, 2018).…”

“…commun.) However, it is a naive belief that smaller reservoirs generate fewer impacts than larger ones (Baumgartner et al, 2018).…”

Peixes a jusante de empreendimentos hidrelétricos no rio Paranaíba, MG: variação espacial e temporal das comunidades, avaliação do monitoramento contínuo e modelo de predição para mitigação de risco na interação peixe-usina

“…Identificar padrões nas assembeias de peixes e os fatores responsáveis por impulsionar suas interações são desafios para ecólogos de sistemas aquáticos, principalmente em ambientes modificados (Baumgartner et al, 2018). Tais modificações alteram as interações interespecíficas, dificultando a previsão da organização dessas assembleias.…”