Short-term changes in energy allocation by Hemiodontidae fish after the construction of a large reservoir (Lajeado Dam, Tocantins River)

Abstract

The present study investigated energy allocation patterns in three fish species from the family Hemiodontidae (Argonectes robertsi, Hemiodus microlepis, and Hemiodus unimaculatus), before and after the construction of Lajeado Dam, Tocantins River, Amazon basin. Changes in the use of energy (between somatic and reproductive processes) were indirectly evaluated by means of temporal variations in fish body condition, feeding activity, visceral fat storage, and reproductive effort. Fish were collected from October 1999 to September 2004, in periods that preceded and followed the construction of the dam. We recorded significant changes in all ecological traits for the three analyzed species (for males and females). In general, there was an intense reduction in reproductive activity after river damming, whereas visceral fat and body condition increased consistently. In contrast, there was no clear trend in feeding activity (i.e., stomach weight), with little changes in species diet during the analyzed period. These results indicate that the impoundment changed the energy allocation process between somatic and reproductive activities, since fish started to allocate energy mainly to somatic processes. These changes may have a negative effect on the persistence of populations in Lajeado Reservoir, because improvements in somatic condition will not necessarily translate into increased fitness.Neste estudo buscou-se avaliar padrões na alocação de energia em três espécies de peixes da família Hemiodontidae (Argonectes robertsi, Hemiodus microlepis e Hemiodus unimaculatus), antes e após a construção da UHE Lajeado, rio Tocantins, bacia Amazônica. Alterações no uso da energia (entre atividades somáticas e reprodutivas) foram avaliadas de maneira indireta, através de variações temporais na condição corporal dos peixes, atividade alimentar, acúmulo de gordura visceral e esforço reprodutivo. Os peixes foram coletados no trecho afetado pela barragem entre outubro de 1999 e setembro de 2004, envolvendo períodos que antecederam e sucederam a formação do reservatório. Registramos alterações significativas nos valores dos atributos medidos, para peixes machos e fêmeas das três espécies analisadas. De maneira geral, houve intensa redução na atividade reprodutiva nos anos que seguiram ao barramento, enquanto que registramos acúmulo de gordura visceral e aumento na massa corporal das espécies. Por outro lado, não houve um padrão claro de variação na atividade alimentar (i.e., peso dos estômagos), assim como registramos pouca alteração na dieta das espécies entre os períodos. Esses resultados indicam que o represamento alterou o processo de alocação de energia entre atividades somáticas e de reprodução, já que os peixes passaram a direcionar a energia adquirida via alimentação principalmente para processos somáticos. Podemos prever, com isso, que as alterações observadas tenham efeitos negativos na persistência das populações em Lajeado, já que o aumento na condição individual não deve acarretar necessariamente em aumentos no fitness dos...

Fish assemblages in Neotropical reservoirs: Colonization patterns, impacts and management

“…hydrological variation) may not complete the reproductive process, mainly during the years following the impoundment. Medeiros et al (2014) reported failed reproduction for Hemiodontidae after the formation of Lajeado Reservoir, Tocantins River, an event that changed energy allocation patterns for these species. However, most of the species that inhabit reservoirs search for lateral tributaries, upstream stretches or other lotic areas for spawning, indicating the dependence on riverine habitats to complete their life cycles.…”

Ecology of Mylesinus paucisquamatus Jégu & Santos, 1988, an endangered fish species from the rio Tocantins basin

“…It is worth noting, however, that several large dams currently regulate the flow regime of the rio Tocantins and some tributaries. These impoundments affected fish populations and assemblage structure Araújo et al, 2013;Medeiros et al, 2014), therefore, it is likely that the distribution of M. paucisquamatus has been also affected. In the area impacted by Tucuruí dam, for example, the species apparently persists in streams adjacent to the reservoir (Ribeiro et al, 1995;Santos et al, 2004;Nogueira et al, 2010), which may work as refuge after the loss of lotic habitats.…”

“…The basin can be divided into distinct geomorphological regions (Ribeiro et al, 1995), with the upper and middle regions characterized by the presence of waterfalls and rapids, and the lower region characterized by lowlands and floodplains. At present, the main channel is regulated by seven large dams (Medeiros et al, 2014), which fragmented the fluvial course, stabilized the water level in the impounded areas and, consequently, changed the natural flow regime and habitat structure in some sections.…”

“…Some studies suggest that it is rare in terms of abundance and spatial occurrence (e.g., Marques et al, 2009;Miranda & Mazzoni, 2009;Claro-Garcia & Shibatta, 2013), currently listed as endangered (category "vulnerable") in the Brazilian official list of endangered species (Ministério do Meio Ambiente, Portaria n° 445, 2014). Although not evaluated by IUCN, the conservation status of this species is matter of great concern, because the construction of dams along the Tocantins caused extensive habitat losses and degradation (Araújo et al, 2013;Medeiros et al, 2014); populations may have been extirpated from some river sections.…”

“…Particularly, the objective of this study was to provide information about (i) population size structure, (ii) abundance patterns along the rio Tocantins and major tributaries, (iii) feeding and (iv) reproductive period. This information may contribute to set management plans to conserve this endangered species, primarily because the rio Tocantins is currently regulated and fragmented by several large hydropower dams (Araújo et al, 2013;Medeiros et al, 2014).…”