The fishery and fishery yield of Hypophthalmus edentatus (Spix, 1829), (Siluriformes, Hypophthalmidae), in the Itaipu reservoir, Paraná state, Brazil

Abstract

Artisanal fisheries conducted in the Itaipu Reservoir were surveyed from 1987-1993 and 1995-1998 to obtain information on landings (yield) and fishing effort used to catch Hypophthalmus edentatus. Historical, structural and functional aspects of the H. edentatus fishery were obtained previoushy. Yield and CPUE (kg/fish.day) of H. edentatus decreased after 1995. The lowest yield value was observed in 1998 (154 tons) and the highest in 1991 (515.3 tons). The effort applied (fishing days) was highest in 1993 (75,890). The lowest vale was registered in 1987 (42,000). The Schaeffer model, adjusted by nonlinear procedure, estimated the maximum sustainable yield (MSY) near 395 tons/year and optimum effort of 66,500 fisherman x fishing days-1. Factors like failures in spawning, decline in food supply, predation and overfishing seem to related to the decrease in yield of H. edentatus. Nevertheless, factors such as algae blooms (Mycrocistis sp.) and use of small gillnet meshes (70mm) in the fishery may also have contributed to the decrease in yield. Another complete evaluation may be necessary because the factors that affect the yield of H. edentatus may have multiplicative effects with possible interactions.