Ecologia de duas espécies de Pachyurus (Perciformes, Sciaenidae) do rio Tocantins, na região represada pela UHE Serra da Mesa, Goiás

Abstract

ABSTRACT. Ecology of two species of Pachyurus (Perciformes, Sciaenidae) from the Tocantins River, in the region impounded by the Serra da Mesa hydroelectric dam, Goiás. Pachyurus schomburgkii Günther, 1860 and P. paucirastrus Aguilera, 1983 occur in the Tocantins-Araguaia basin, where the latter is endemic. The species were found in the upper Tocantins, in the region where it was impounded by the Serra da Mesa hydroelectric dam. Fourteen sites were sampled but both species were restricted to two sites (FU and PG) located downstream from the dam. Fishes were bimonthly captured from December 1995 to December 2002 with standardized gillnets. We present data on the distribution, diet, physiological condition and the reproductive status of these species, and focus on the alterations related to the impoundment. Most specimens were adult, and the number of reproductive individuals decreased after damming. Species were classified as benthic invertivores, feeding mainly on immature insects. Niche breadth was significantly higher to P. paucirastrus, and, for both species, during the pre-impoundment phase. Interspecific diet overlap was high; however, resource partitioning was more pronounced in the site immediately downstream from the dam (FU) than partitioning in the more distant site (PG). Values relative to the condition factor indicated that P. schomburgkii must have profited more effectively from the available resources after the environmental changes than P. paucirastrus. Thus, factors related to feeding might have contributed to the disappearance of this species after the beginning of power plant operation. Pachyurus schomburgkii seems to have had a better adjustment to changes, and was more persistent in the area after the damming; however, it remained restricted to the more distant site, where it had been occasionally captured until it was no longer found, approximately four years after dam closure. Considering that many impoundments are planned to the rio Tocantins, we recommend further studies about P. paucirastrus in other stretches of the basin, in order to evaluate the conservation status of this species.KEY WORDS. Pachyurus, biology, diet, impoundment, Tocantins River. RESUMO.Pachyurus schomburgkii Günther, 1860 e P. paucirastrus Aguilera, 1983 ocorrem na bacia Tocantins-Araguaia, sendo a segunda endêmica da bacia. Ambas foram encontradas na região do alto Tocantins, onde este foi represado pela usina hidrelétrica Serra da Mesa, tendo sido capturadas somente em dois de 14 pontos amostrados, sendo ambos (FU e PG) a jusante da barragem. Os peixes foram amostrados bimestralmente com redes de espera padronizadas entre dezembro de 1995 e dezembro de 2002. São apresentados dados de distribuição, dieta, condição fisiológica e estado reprodutivo das duas espécies, focando possíveis modificações em decorrência da instalação da barragem. A maioria dos indivíduos capturados eram adultos e o número de reprodutivos diminuiu após o represamento. As duas espécies foram classificadas como invertívoras bentônicas, alimentan...

Feeding ecology of Pachyurus bonariensis Steindachner, 1879 (Sciaenidae: Perciformes) in the Ibicuí River, Southern Brazil: ontogenetic, seasonal and spatial variations

“…The main items found by Fugi et al (2007) were also the most important ones here, however two others insect orders were also important: Odonata and Trichoptera. Pacheco et al (2008) also found an insectivorous diet for P. schomburgkii Gunther, 1860 andP. paucirastrus Aguilera, 1983.…”

“…paucirastrus Aguilera, 1983. The predominance of aquatic insects in the food of fish is common in freshwater communities (Sabino and Castro, 1990;Aranha et al, 2000;Abes et al, 2001;Andrade and Braga, 2005;Pouilly et al, 2004;Braga, 2005;Fugi et al, 2007;Pacheco et al, 2008), making the insect larvae a very important food category for fish (Zavala-Camin, 1996). Certain benthic insects, such as Diptera larvae and Ephemeroptera, are abundant in rivers with sandy bottoms (Braga, 2005) such as the Ibicuí River.…”

“…Freshwater sciaenids consume mainly fish and insects (Mourão and Torres, 1984;Hahn et al, 1997Hahn et al, , 1999Alvim and Peret, 2004;Bennemann et al, 2006;Fugi et al, 2007;Pacheco et al, 2008). It can be an adaptation of the species that invaded freshwater to the low availability of crustaceans and great availability of insects in comparison to marine habitats.…”

“…The most common differences are ontogenetic, seasonal and spatial, and are reported for a large number of species (Aranha et al, 2000;Lucena et al, 2000;Abelha et al, 2001;Mazzoni and Rezende, 2003;Araújo et al, 2005;Barreto and Aranha, 2006;Rezende and Mazzoni, 2006;Viana et al, 2006;Fugi et al, 2007;Pacheco et al, 2008). The two last sources of variations, seasonal and spatial, are primarily related to changes in food resource composition and availability, which are associated with productivity variations and physicochemical changes in aquatic ecosystems.…”

“…Among these genera, six are restricted to freshwater and four, Pachyurus, Pachypops, Plagioscion and Petilipinnis, are endemic to South America (Casatti, 2003). The food items most often consumed by members of this family are benthic animals such as crustaceans, polychaetes, mollusks, insects and small fish, and sometimes algae (Mourão and Torres, 1984;Lunardon, 1990;Vazzoler, 1991;Hahn et al, 1997;Figueiredo and Vieira, 1998;Vendel and Chaves, 1998;Hahn et al, 1999;Soares and Vazzoler, 2001;Alvim and Peret, 2004;Branco et al, 2005;Bennemann et al, 2006;Fugi et al, 2007;Pacheco et al, 2008). The sciaenid Pachyurus bonariensis occurs naturally in the rivers of the Paraná-Paraguay-Uruguay system, downstream from the Itaipu Reservoir, including Argentina, Brazil, Paraguay and Uruguay (Casatti, 2001) The P. bonariensis diet was studied once, in two lakes (locally called bays) of the Pantanal, where it had a diet composed mainly of Chironomidae and Ephemeroptera, with important ontogenetic shifts (Fugi et al, 2007).…”