Assembléias de peixes em lagos de várzea situados em duas unidades geomorfológicas no período de seca, região de Itacoatiara, Amazonas

Abstract

Few studies have been conducted on the fish fauna during the dry season in the Amazon floodplain lakes, despite the actions of fishing and environmental changes in lakes. This result in lack of information on patterns of organization of the fish fauna that enable a better understanding of the mechanisms that act on it, and that could be used in management strategies. Thus, the work proposes to study the fishes in floodplains lakes located in the bar-and-meander plains and flood deposits units during dry water period, identifying the abiotic factors (local and regional) that influence on the structure of assemblages fish. The fish were collected with gill nets during the dry period between 2002 and 2005, in Itacoatiara, Amazonas. In the bar-and-meander plains and flood deposits the physico-chemical variables (oxygen, temperature, pH, electrical conductivity and depth) and geomorphological (distance from river, lake area and geomorphological unit) were the abiotic factors measured. We also analyzed the descriptors of assemblage structure (richness, diversity index, evenness, dominance, catch per unit effort in number of individuals (CPUEn) and weight (CPUEw) structure and length). To evaluate the similarity in the fish species composition between bar-and-meander plains and flood deposits was used Correspondence Analysis (CA); to determine if fish size was different between the two units was used test t e Kolmogorov-Smirnov; and to assess the influence of physico-chemical and geomorphological descriptors in the assemblage structure was used covariance analysis (ANCOVA). In bar-and-meander plains were collected 3051 and 224,080.72g of fish, a total of 86 species. In flood deposits, were captured 2334 and 216,314.65g of fish, a total of 108 species. The fish fauna was dominated in terms of individuals number and species composition by Characiformes, Siluriformes and Perciformes. Acestrorhynchus falcirostris, Acestrorhynchus falcatus, Pellona flavipinnis, Moenkhausia. lepidura, Schizodon fasciatus, Potamorhina latior, Hemiodus immaculatus, Hemiodus sp. “rabo vermelho”, Pygocentrus nattereri, Tracheliopterus galeatus, Lycengraulis sp. Triportheus auritus, T. angulatus, Plagioscion squamosissimus e Rineloricaria sp. can be regarded as the most important in the fish fauna composition, and was similar between the both places. The catch per unit effort in number and weight was higher in bar-and-meander plains, and this reflects the high number of specimens of migratory species, medium-sized this place. Diversity was highest in flood deposits, considering that the species distribution was homogeneous in both units, this value reflects the value of dominance of the fish, which was higher in the bar-and-meander plains. Despite the reduction of the flooded areas that affect the heterogeneity of habitats, drought remains a flooded area in the lakes, which explains the high diversity of fish. And the analysis relating to diversity in weight (H'w) of fish assemblages with physical-chemical and geomorphological variables point out the depth, pH and oxygen concentration influencing the assemblage structure in lakes. The total catch weight (CTw) was influenced by regional (geomorphological unit and the lake area) and local factors (depth and electrical conductivity). Thus, the most significant variable for the structure of fish assemblages in lakes of the bar-and-meander plains and DIF was the depth. The results of this research should have a decisive role in the improvement of local and community management as a viable option for conservation of fishing resources in the Amazon.