Temporal variation in yield and composition of the artisanal fishery of the upper Paraná river, PR - Brazil: chronic effects of impoundments

Abstract

The large number of dams in the upper Paraná River basin caused fragmentation of rivers, changing the longitudinal migratory fish process and patterns of hydrologic connectivity, besides modify the specific composition and reduce the biomass caught by artisanal fisheries, activity that generates jobs and income for the families of the region. This paper aims to characterize artisanal fisheries developed in the lower region of the upper Paraná River floodplain, emphasizing the negative effects of hydrologic alteration on composition and efficiency of catches. Total landing data (t) and CPUE (kg fisherman^-1 day^-1) were analyzed between years 1987 and 2005. The differences in CPUE of the main species BEFORE and AFTER the closure of Porto Primavera Dam were assessed with Mann-Whitney (U) test. The temporal variation (years) in species composition was assessed using MDS; the differences between the groups was tested by Analysis of Similarity (ANOSIM) and the contribution of species to the ordination of the year was verified through similarity percentage analysis (SIMPER). Catches ranged from 242.8 tons (1990) to 35.6 ton (1995) with a tendency toward in CPUE reduction of the species of higher commercial value after the year 2000. Alteration in the species composition occurred in catches after 2000, predominating sedentary species and with reproduction independent of the hydrological cycle. The results indicate the need for fishery management to prevent overfishing of the current target fish species and increased river flow for the recomposition of migratory fish stocks.