Extreme events and ichthyofauna: case report of a neotropical river

Resumo (EN)

The increasing frequency and intensity of extreme weather events and their impact on
aquatic ecosystems and fish species is concerning. This manuscript reports and analyzes two events, a drought in 2019 and a flood in 2024, providing valuable insights into the consequences of these events. The rescue of 269 individuals of 19 fish species during the 2019 drought highlights the significant impact of the extreme conditions on the ichthyofauna. Rising temperatures, isolation, and habitat fragmentation must have posed severe challenges for the fish species during this period. On the other hand, the observation of 53 dead individuals of 5 species during the 2024 flood indicates the detrimental effects of this event on the fish population. The association of mortality and dispersal of several species with the existing dam further underscores the complexity of the challenges faced by fish during extreme flood events. The correlation between rainfall, river regime, and the impact of land use and occupation provides an important context for understanding the dynamics of these extreme events. The low rainfall during the 2019 drought and the gradual increase in rainfall between 2022 and 2024 leading to the flood demonstrate the significant role of precipitation patterns in shaping the outcomes for fish species. Additionally, the analysis of land use and occupation, particularly the substantial increase in urbanization in the drainage basin over the last 30 years, highlights the human-induced factors contributing to the stress on aquatic ecosystems. Both extreme floods and droughts have significant implications for fish species. Extreme floods can alter riverbeds, cause direct mortality, and disrupt isolated populations, while extreme droughts can lead to fish kills, and habitat fragmentation, and exacerbate environmental stressors. This analysis emphasizes the urgent need for comprehensive measures to mitigate the impact of extreme weather events on aquatic ecosystems and fish species. Addressing factors such as land use and occupation, water management, and climate change adaptation strategies is crucial for promoting the resilience of fish populations in the face of ongoing environmental challenges.