Climate change and the heat summer 2018: impacts on freshwater fish populations

The year 2018 has been the warmest year since 1881, when regular measurements started in Germany. It has also been one of the driest years, with ten months in succession being too dry. This combined heat and drought wave caused severe impacts on most freshwater ecosystems. It led to overheated water bodies and critically low water levels in many lakes and rivers, up to completely dried out riverbeds. Often, this resulted in high fish mortality. Fish-stock surveys in Baden-Wurttemberg showed a significant decline in the overall abundance of fish species. Especially the proportion of cold-adapted fishes decreased. However, in some parts, warm-adapted carp-like species became more abundant. Ongoing research will determine if fish stocks are able to recover from this record heat summer or if future weather extremes will further exacerbate the situation. To mitigate negative impacts of climate change on the local fish fauna and aquatic ecosystems, possible management measures are discussed.