Dinámica estacional de la ictiofauna de Laguna Alsina, provincia de Buenos Aaires, Argentina

This study aims at characterizing the seasonal dynamics of the ichtyofauna of Alsina lagoon which belongs to the Encadenadas del Oeste (Province of Buenos Aires, Argentina). Fish sampling was performed on a three-month basis, from April 2007 to March 2008, using gill nets and a trawl net. Diversity (H’) and species richness were calculated for every sampling station and for each season. Differences in H´ values were analyzed via ANOVA. Relative abundance in number was estimated with net mesh capture. Capture per unit effort (CPUE) was calculated considering the fishing night as unit effort and the size structure of the dominant species was described. A total of 8643 individuals belonging to 14 species were captured. Species richness varied from 8 to 11. H´ evidenced no significant differences among places (p=0.15) although differences were recorded all over the year (p=0.001). H´ was highest in autumn (2.23) and lowest in spring (0.96). In autumn, the dominant species were Odontesthes bonariensis (34%), Parapimelodus valenciennis (32%) and Oligosarcus jenynsii (28%). In winter, the dominant species were only O. bonariensis and O. jenynsii, both representing more than 90%. A significant increase in CPUE was observed in pejerrey (O. bonariensis). Dominant size ranges were 15-17 and 20-25 cm Lst in O. bonariensis and 17-23 cm Lst in O. jenynsii. It can thus be concluded that Alsina lagoon has a key role as a biodiversity reservoir of continental waters. The ichthyc community has undergone modifications, of which the most relevant include: disappearance of P. valenciennis and increase of O. bonariensis. The recuperation of O. bonariensis stock therefore guarantees a promissing future for this environment which formerly reached highest productivity in Encadenadas del Oeste system.Instituto de Limnología "Raúl A. Ringuelet