Evaluation of factors associated with dynamics of Cichla ocellaris invasion of the Upper Parana ́ River floodplain system, Brazil

Abstract. Invasion byCichla ocellariswas studied in the Upper Parana ́ River floodplain. Generalised linear models and the Akaike Information Criterion (AIC) were applied to standardised gill-net catch data (CPUE), with years, rivers, secchi depth, and their respective interactions. Generalised additivemodels andAICwere used to evaluate relationships of CPUE for C. ocellariswith standard length, sampling year and secchi depth. C. ocellariswas first recorded in 1992 in the Paraná and Ivinheima Rivers. Nevertheless, the CPUE of individuals was very low in the latter until 2000, and the species was not recorded from the Baı́a River until 2000. In 2001, CPUE of C. ocellaris greatly increased (from 20 to 140) in all three rivers, and this coincided with changes in hydrology and suspended sediment. Greater secchi depth is thought to benefit foraging by these visually oriented, diurnal piscivores. The estimated annual growth rate for local populations was 21 % for the Paraná, 42 % for the Ivinheima, and 73 % for theBaı́a Rivers. Consequently, relative to other populations,C. ocellaris of the Baı́a River and, to a lesser degree, the Ivinheima River, appear to be less influenced by density-dependent factors given their more recent invasions of those areas