Short-term effects of Storm Daniel on Salmo farioides (Karaman, 1938) in a high-gradient stream

Climate change is expected to increase the magnitude, frequency, and intensity of extreme natural phenomena such as droughts and floods. These events can have devastating impacts on aquatic biota, thus there is a dire need to assess species' natural dynamics and to incorporate them into species' conservation actions and flood management decisions. In September 2023, an extreme meteorological event (Storm Daniel) occurred over the eastern Mediterranean, causing unprecedented high flooding events in many streams and rivers of central Greece. Almost 2 months after the event, we investigated the effects of the storm on Salmo farioides in a high-altitude stream (Kraniotiko stream, Acheloos river basin) by comparing pre-flood (June and August 2023) with post-flood (October 2023) data on fish population abundances and size structure. Our results provide direct evidence that the population of S. farioides was almost wipedout from the investigated stream, as post-flood fish densities were 9.3% of the pre-flood data (August) densities. Small-sized individuals (6-10 cm) were extirpated, indicating a 99% decrease during the post-flood period, totally reversing the increasing trend observed from June to August (pre-flood period). In conclusion, the profound and rapid decline observed in the population of S. farioides following the extreme flooding event highlights the urgent need for proactive conservation measures and adaptive management strategies to safeguard vulnerable aquatic species in the face of escalating climate-related challenges.