Composição e distribuição espaço-temporal da ictiofauna dulcícola da bacia Rio Mamanguape - Paraíba - Brasil

Abstract

The South America is the ichthyic richest area of the Neotropical region, the richest fish fauna in the world. The periphery of South America, however, is characterized by a low ichthyic richness, including the semi-arid regions of the continent, as the Caatinga’s domain. The Mamanguape River basin is part of this context, its headwaters and middle portion running in the Caatinga both wetter or drier, and its lower portion runs in the Atlantic Forest area. As a result the main course at the upper and lower portions, and most of the tributaries are intermittent. The study aims to describe the composition of the freshwater fish fauna of Mamanguape River basin and assess the spatiotemporal distribution of the recorded species and environmental variables associated with the main course. The sample design was established through the distribution of fixed points of seasonal collection (dry and rainy season) in the three stretches of the main curse (High, Medium and Low), six points by stretch, totaling 18 fixed points, and the application of "AquaRap" methodology in the tributaries, in order to archive a wide survey of the basin, within the limits of the study (20 points were added). The 38 collection points were visited between August, 2015 and March, 2016. The specimens were collected with the use of beach seine, casting net and deep net, standardized on Fixed Points through number of tows; in tributaries the effort was standardized following AquaRap methodology. Available secondary data were obtained from UFPB’s Ichthyological Collection (the only collection holding specimens from Mamanguape River basin) were used to build the Systematic List of the Mamanguape River basin’s ichthyofauna. Environmental descriptors were taken at each fixed point during dry and rainy seasons, in order to test them as possible predictors of the fish fauna’s distribution. Statistical analyzes were made in the PAST and R software. 29 species were recorded in the field and two species from secondary data, totaling 31 fish species distributed in 26 genera, 16 families and six orders. Of those, one is endangered (Apareiodon davisi) and three are introduced species (Poecilia reticulata, Cichla cf. monoculars, Oreochromis nilotica). The Principal Component Analysis (PCA) showed a marked variation in environmental descriptors between the dry and rainy seasons, but found that, considering the changes of the longitudinal river axis, only in the upper stretch was registered significant difference when compared the middle and lower sections, which were similar to each other. Among the recorded species, 28 were recorded in the main course of the basin. The greater dominance (abundance) of species was recorded in the rainy season, and the greatest diversity in the dry season. Ordination analysis from Non-metric Multidimensional Scaling (nMDS) indicated that there is no significant variation in faunal composition between dry and rainy seasons, but showed that the three stretches of the river significantly differs to each other, something also demonstrated by the used ecological indices. The altitude, the current speed and the dissolved oxygen significantly influenced the distribution of fish populations, according to Canonical Analysis of redundancy (RDA). The timescale considered here offers no basis for assessing the distinctions of the ictiofaua between sampling periods. The spatial differences in species composition suggest the existence of environmental heterogeneity between different stretches of the river. It is recommended to carry out work that may consider scales not considered in the present study, so that they can propose measures of conservation for the fish fauna of the study area.