Estrutura de comunidades de peixes de igarapés de três pequenas bacias de drenagem sob uso de Agricultura Familiar no Nordeste Paraense

Abstract

Stream fish species can be distributed in space and time and in an organized pattern, which can be observed on the association of groups of species and their relationship to certain habitats. The reduced number of studies and the scarce knowledge on the aquatic fauna in Amazon contribute to the under-estimation of the magnitude of impacts upon lotic habitats and stream fish fauna. The Bragantina Region, in the northeast portion of Pará, is an example of an old agricultural frontier in the Amazon. Smallholder farming in the area is expressive, the main cultures are corn, caupi, and cassava, and semi-perennial cultures, such as “maracujá” (passion fruit) and “pimenta-do-reino” (black pepper). The areas of familiar production are a dominant feature of the landscape, thus contributing to most of the soil and aquatic ecosystem degradation. Aiming at the description of stream fish communities and its relations to environmental variables, a two-year study was carried out in eight reaches of three streams located in this region: Cumaru, São João and Pachibá streams. After nine monthly collections, 2.117 fishes were collected, distributed in seven orders, 13 families, 27 genera and 43 species. The most abundant species in all samples was Hypessobrycon heterorhabudus, totalling 337 individuals, followed by Bryconops caudomaculatus, with 326 individuals. The species richness was highest in a Pachibá stream reach (IGPA-B), with 21 species. Simpson’s diversity index showed the highest species dominance in a Cumaru stream reach, while Shannon’s diversity index showed that the IGPA-B had the greatest diversity. Iguanodectes spirulus was the most constant species, occurring in 50% of samples. The similarity between the environments showed that the distribution of species followed a longitudinal pattern instead of a geographic pattern. Land use, specially small farms, did not affect the ichthyofauna, since the low intensification of this activity still permit some integrity to aquatic ecosystem. However, as agriculture system intensification increases in the future, we do not know what will be the ecosystem response.