Three seine nets sampling applied to the littoral zone of two Brazilian tropical rivers with reduced velocity ( Brazil)

Abstract

Three seine nets (TSN method) laid simultaneously from the bank to form concentric semicircles (enclosing an area of 350 m2) and hauled one after the other were employed for the removal fishing technique in littoral zones with reduced velocity in the Parana River catchment. Fish density was estimated using the Zippin maximum likelihood method. The efftciency of this TSN method, estimated by two different indexes was not diminished by the size of the populations, but was limited by the kind and amount of obstacles on the bottom (submerged macrophytes, branches, mud) and the habitat preferences of the fish taxa. TSN was found to give best results for pelagic fishes, slightly less good for bentho-pelagic, and less good again for benthic ones, although it was not altogether unsatisfactory for quantitative research on fish populations.