Gradientes espaço-temporais da pesca artesanal no reservatório de Itaipu, Paraná, Brasil.

Abstract

It is expected that the longitudinal limnological gradients described for reservoirs have great implications for the composition and yield of multispecific fisheries practiced in this type of environment, directly and indirectly affecting the operational strategies for the collection of the species. Recognition of patterns of spatial and temporal variation of stocks and their form of exploitation is fundamental to the rationalization of fishery management. It is, however, a complex task given the large number of variables and the physical, biological and socioeconomic interactions involved. Daily landing data from 12 fisheries along the Itaipu reservoir over a period of 11 years are analyzed in this study. Uni and multivariate analysis techniques are used to identify (i) spatial-temporal patterns in the composition of the fish and in the yield of the fishery and (ii) longitudinal gradients in the operational strategies used in fishing. The results are discussed in light of longitudinal and temporal limnological gradients, species life strategies and competitive uses of the basin upstream. Significant correlation was verified between sedimentation rates, considered a synthesis variable of the limnological conditions, and yield of the 10 main species (90% of the total catch). Of these species, eight showed significant longitudinal gradients in abundance. Three of them concentrated in the fluvial zone, one in the lacustrine, three in the fluvial-transitional and one in the lacustrine-transitional. Diet requirements (autochthonous and allochthonous resources) and migratory behavior were considered the most adequate terms to explain these patterns. The marked decline in the fishery yield was attributed to the fall in the CPUEs of the two most caught species, that were, perna-de-moça Hypophthalmus oremaculatus in the lacustrine zone (trophic state reduction in the reservoir, recruitment overfishing) and armado Pterodoras granulosus in the fluvial zone (regulation of the floods on the floodplain upstream from the operation of new reservoirs, growth overfishing). Three fishery strategies were observed: (I) cascudo-preto Rhinelepis aspera fisheries in the fluvial zone using casting nets and wooden boats propelled by a stationary (center) motor (10 to 12 HP), (II) Hypophthalmus oremaculatus fisheries in the transition and lacustrine zones with gillnets, wooden boats driven by oars or a rabeta motor (3.5 to 4 HP) and (III) Pterodoras granulosus and jaú Zungaro jahu fisheries in the fluvial zone carried out with fish-hooks, wooden boats and a stationary (center) motor (10 to 12 HP). It was verifield the importance of the fisheries in sustaining families marginalized from other sectors of the economy and their regulation and rationalization in the operation of the reservoirs upstream to insure the occurrence of floods on the floodplain upstream.