Abstract The present study was based on the analysis of 10,467 trawls of the industrial piramutaba (Brachyplatystoma vaillantii) fishing fleet of the Brazilian state of Pará, which were mapped by onboard GPS loggers (between February 2008 and September 2011) and the PREPS data from 40 vessels which were tracked by this system between 2008 and 2011. The variation in the mean monthly CPUE, based on Lomb’s periodogram, revealed a well-defined and constant cycle with a duration of approximately one year. Three environmental factors influenced this cycle. The El Niño 3.4 index had a negative correlation with the CPUE of the piramutaba fishery, with a time lag of 15 months, while monthly rainfall and the mean discharge of the Amazon River correlated strongly (r=0.89 and 0.87, respectively; p<0.001) with the CPUE, with time lags of 12 and 11 months, respectively. The spatiotemporal analysis of the distribution of the activity of the piramutaba fishing fleet indicated that the most intense area of operation of the fleet lies between latitudes 00º N and 02° N, and longitudes 047º40’ W and 049º40’ W. This area was divided into four geographic quadrants, although fishery operations were concentrated in only three of these quadrants. The study proposed a quadrimester fishing cycle with zoning in three of the quadrants, where fishing would be permitted for four months (occupation period), followed by an 8-month rest period for the recuperation of stocks, aiming at the sustainability of this fishing exploration.

Abstract Patterns of beta diversity of plankton communities in rivers have been mainly determined by hydrological factors that alter the dispersion and composition of species and traits. Rotifers in the Guamá River (eastern Amazonian River) were sampled (monthly between October 2017 and June 2019) to analyze the temporal variation of taxonomic and functional beta diversity and its partitions (turnover and nestedness) as well as the effects of temporal, environmental, and seasonal dissimilarities. Taxonomic turnover and functional nestedness over time were observed as well as functional homogenization, which was arguably due to the hypereutrophic condition of the river. There were no seasonal differences in taxonomic and functional beta diversity probably due the low environmental dissimilarity. This study demonstrated that this Guamá River stretch presented low environmental dissimilarity and hypereutrophic waters, which benefited the establishment of a community of species with high taxonomic turnover over time, but with low functional dissimilarity and loss of some functions related to the functional traits evaluated in the ecosystem. It is important to point out that temporal studies should evaluate both taxonomic and functional aspects of communities, mainly because the effect of environmental changes may be more noticeable at the functional level of communities.