Influence of the river flow on the structure of fish assemblage along the longitudinal gradient from river to reservoir

Bianca De Freitas Terra,Francisco Gerson Araújo,Alex Braz Iacone Santos

doi:10.1590/s1984-46702010000500010

Abstract

Changes in fish assemblage structure along a longitudinal gradient of the Paraiba do Sul River and Funil reservoir were studied to detect distribution patterns and the seasonal influence of the inflowing river. Fish were caught by gill nets in three zones (riverine, transition and lentic) during two seasons (dry and wet). A total of 3,721 individuals were captured, comprising five orders, 14 families, 27 genera and 33 species. Five species were non-native and amounted to 17.7% of the total number of individuals. The 10 most abundant species were used to assess spatial-temporal patterns. Plagioscion squamosissimus (Heckel, 1840), Oligosarcus hepsetus (Curvier, 1829) and Metynnis maculatus (Kner, 1858) were widely distributed in both seasons. Astyanax bimaculatus (Linnaeus, 1758), Cichla kelberi Kullander & Ferreira, 2006 and Geophagus brasiliensis (Quoy & Gaimard, 1824) had higher abundance in the dry season, occurring mainly in the lentic zone. By contrast, the benthopelagics Pimelodus maculatus La Cepede, 1803 and Astyanax parahybae (Eigenmann, 1908) and the benthics Hoplosternum littorale (Hancock, 1828) and Hypostomus auroguttatus Kner, 1854 had higher abundance in the wet season, with the two first species occurring mainly in the riverine zone, and latter two species in the transition zone. The highest diversity for both seasons was recorded in the transition zone, which is an ecotone that allows the co-existence of both riverine and lentic species. A major shift in assemblage structure occurred along the longitudinal gradient due to changes in discharge of the inflowing river, with increased fish abundance in the riverine zone caused by increased habitat availability in wet season, and the reverse of this situation in the dry season.

Highlights

Water flow represents the main force behind freshwater ecosystems (POFF et al 1997), determining the distribution, abundance, and diversity of stream and river organisms (SCHLOSSER 1982, POFF & ALLAN 1995, WARD et al 1999, NILSSON & SVEDMARK 2002)
The present study aimed to describe the patterns of diversity in the fish assemblage of the Paraíba do Sul River – Funil reservoir system along three zones and two seasons
A major difference in the structure of the fish assemblage was detected along the longitudinal stretches of the Paraíba do Sul – Funil reservoir system, featuring a more abundant and rich assemblage in the riverine zone during the wet season, and the opposite situation in the dry season

Summary

Introduction

Water flow represents the main force behind freshwater ecosystems (POFF et al 1997), determining the distribution, abundance, and diversity of stream and river organisms (SCHLOSSER 1982, POFF & ALLAN 1995, WARD et al 1999, NILSSON & SVEDMARK 2002). Seasonal variations in water level have direct influences on the structure of species assemblages along the longitudinal gradient due to changes in water features (e.g. transparency and allochthonous material input), habitat availability (mainly in the riverine zone) and food resources. These new environmental conditions in impounded areas, which include increased water transparency, favor the colonization by opportunists (e.g. characins) and nonnative carnivores (e.g. cichlids) that make more intensive use of vision. We attempted to establish correlations between environmental alterations caused by changes in discharge of the inflowing river and shifts in the structure of the fish assemblage

Methods

Results

Conclusion