Exploring the effect of strong hydrological droughts and floods on populational parameters of Semaprochilodus insignis (Actinopterygii: Prochilodontidae) from the Central Amazonia

In Amazonia, commercially important fish species—such as Semaprochilodus insignis—are highly dependent on the hydrological regime, that is, the flood pulse. As waters begin to rise, this species migrates from nutrient-poor rivers to nutrient-rich rivers via their associated floodplains, using such habitats as spawning and nursery grounds. However, strong droughts or floods may alter such dynamics. Therefore, this study was aimed at answering the following questions: (1) Is there any relationship between the flood amplitude and the growth of S. insignis caught in the lower Solimoes River? (2) Is there any relationship between the yearly maximum river level and the fishing mortality of S. insignis caught in the upper Amazon River? Growth parameters were estimated using the ELEFAN routine. Explanatory variables hypothesised to be relevant predictors of populational parameters were tested using multiple linear models. A 2-year-lagged effect of flood amplitude resulted in a decline in the growth of S. insignis. In contrast, in relation to years with the highest maximum water levels, an immediate and 1-year-lagged reduction in fishing mortality was observed. Therefore, despite the negative impact of years with high flood amplitude on the growth of this species, it is apparent that a sequence of years with La Nina influence helped in the recovery of S. insignis.