Assessing fish assemblages similarity above and below a dam in a Neotropical reservoir with partial blockage

Abstract

Damming rivers disrupts the water flow and changes the ichthyofauna organisation. We investigated an impoundment with permanent connection and homogeneous environmental conditions between the zones above and below the dam. Temperature was comparatively higher during wet season irrespective of zone, and both zones had higher dissolved oxygen, conductivity and transparency in the dry season. A total of 1687 individuals comprising 27 species were collected in the downriver zone, while the reservoir had 879 individuals and 23 species. Each zone had different fish assemblage composition and structure, but assemblages were not explained by the examined environmental variables (r 2 = 0.08; p = 0.307). Migratory species such as Pimelodus maculatus, Pimelodus fur, Leporinus copelandii and Prochilodus lineatus were the most affected, and probably are prevented to perform upriver migrations. On the other hand, lentic adapted species such as G. brasiliensis, Hoplias malabaricus and Hoplosternum littorale successfully colonised the reservoir. Therefore we conclude that the presence of the lateral hydrological connectivity alone does not guarantee the ecological connectivity since fish assemblage similarity differed between the two zones. Fish passage facilities should be monitored and managed to evaluate and improve their functionality.Keywords: reservoirs, ichthyofauna, fish migration, river connectivity, Paraíba do Sul River.Avaliando a similaridade das assembléias de peixes acima e abaixo de uma barragem de um reservatório Neotropical com obliteração parcial Resumo O represamento de rios interrompe o fluxo de água e altera a organização da ictiofauna. Nós investigamos um represamento com conexão hidrológica permanente e homogêneas condições ambientais entre as zonas acima e abaixo da barragem. A temperatura foi comparativamente mais elevada na estação chuvosa independente da zona, e ambas as zonas apresentaram maior oxigênio dissolvido, condutividade e transparência na estação seca. Um total de 1687 indivíduos compreendendo 27 espécies foi coletado na zona de rio abaixo da barragem, enquanto 879 indivíduos e 23 espécies foram registrados no reservatório. Cada zona teve assembléias de peixes com diferente composição e estrutura, mas as assembléias não foram explicadas pelas variáveis ambientais examinadas (r 2 = 0.08; p = 0.307). Espécies de peixes migratórias, como Pimelodus maculatus, Pimelodus fur e Prochilodus lineatus foram as mais afetadas, e, provavelmente, são impedidas de realizar migrações rio acima. Por outro lado, espécies adaptadas a ambientes lênticos tais como G. brasiliensis, Hoplias malabaricus e Hoplosternum littorale colonizaram o reservatório com sucesso. Portanto, concluímos que a presença da conectividade hidrológica lateral sozinha não garante a conectividade ecológica já que a similaridade da assembleia de peixes diferiu entre as duas zonas. A passagem de peixes deve ser monitorada e gerenciada para avaliar e melhorar a sua funcionalidade.Palavras-chave: reservatórios, ictiofauna, migração d...

Unraveling trait‐based fish community assembly in tropical reservoirs

“…This scenario reinforces the importance of the physical features of reservoirs to determine the functional space to be filled by different fish species. Likewise, these results show that the loss of hydrological connectivity disrupts population flows within the riverine system, which together with the introduction of non‐native species culminate in highly distinct taxonomic structures even in reservoirs close to each other (Araújo et al, 2013; Pelicice et al, 2015). The similar trends observed per season (dry or wet) revealed that similar assembly processes operate in all reservoirs over short‐term temporal dimensions, reinforcing the strength of spatial patterns.…”

“…River damming creates new ecosystems, changing physical and chemical characteristics by transforming lotic systems into lentic habitats (Agostinho et al, 2016; Granzotti et al, 2018; Tundisi & Matsumura‐Tundisi, 2003). These changes promote habitat loss, changes in resource availability, and limitation of riverine connectivity, increasing extinction risk of endemic taxa and favoring invasions by non‐native species and prevalence of generalist species (Araújo et al, 2013; Fitzgerald et al, 2018; Liermann et al, 2012). Dams thus can act as environmental filters strongly selecting functional traits, and generating long‐lasting changes to the structure of fish assemblages (Lima et al, 2018; Oliveira et al, 2018).…”

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“…Among them, river damming is one of the most influential anthropogenic modifications to riverine ecosystems (Santos & Araújo, 2015). It affects many key aspects of the ecosystem such as hydrologic connectivity, which is crucially important to fish and other aquatic organisms (Araújo et al, 2013). Impounded streams rapidly change their characteristics from being relatively shallow flowing habitats to being deeper stagnant watercourses, which native stream fishes have likely not experienced during their evolution (Baxter, 1977).…”