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

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Abstract
River damming alters the physical–chemical variables of water and often causes compartmentalisation of aquatic habitats. Seasonality can add complexity to the longitudinal compartmentalisation. The spatial and temporal effects of these two phenomena on the structure of ichthyofauna from a tributary under the influence of damming were evaluated, based on the following hypotheses: (1) transition habitats have the greatest species richness; (2) community similarity decreases with increasing distance between sites; (3) conservation of free‐flowing areas upstream reservoir contributes to the maintenance of migratory species. To evaluate the effects of these two phenomena, twelve monthly fish samples (September/12 to August/13) were performed with gillnets in three sample areas distributed longitudinally in the tributary. Limnological variables were measured in the same sample areas to confirm compartmentalisation. We observed three distinct limnological compartments (lotic, transition and lentic), with increase differentiation during the rainy season. This compartmentalisation influenced fish fauna where localised communities exhibited different compositions among the three sampled habitats. During the rainy season, these differences become pronounced, with transition habitat showing greater species richness than the others. More pronounced differences in species composition and structure in extremes sampling sites were also observed. Migratory fish presented higher proportion of fish composition in lotic habitat. In conclusion, damming and seasonality acted concomitantly as modulators of fish fauna in a tributary influenced by damming. However, compartmentalisation of habitats was the primary driver of ichthyofauna community structure with the rainy season increasing differences in community composition.
Funding Information
  • Conselho Nacional de Desenvolvimento Científico e Tecnológico (ABN: GD 140360/2011-5, DFS: GM 141526/2015-7, JQS: GM 130098/2011-6, GD 140346/2013-9, BEX 2574/)
  • Fundação de Amparo à Pesquisa do Estado de São Paulo (Finnancial support 2011/24159-3)
  • Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (FPL: GD 141941/2012-0)

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