The threat status of plants and animals has been recorded in Red Lists of threatened species for over four decades. Although these lists are not legally binding, they are an established tool in conservation practice, guiding landscape planning, impact assessment, and nature and species conservation. The basic idea is relatively simple. Species with highly specific environmental requirements or those that are very sensitive to interference are usually the first to be affected by disturbances. This leads to their decline or disappearance from an area. Conversely, the presence of threatened species in an area suggests that even sensitive species may still find suitable conditions to live in, which is a positive sign. For fish especially, the status of a threatened species’ population can indicate the quality of the water habitat.
The larger the area covered by a Red List and the greater the threat to a species, the more valuable and widely important their populations are considered in species conservation. Red Lists are helpful for assessing environmental impacts because they are regularly revised and updated with the latest population data. They also provide a clear and reliable classification of species.
The fourth update of the Red List of fish and lampreys, discussed here, evaluates the current threat levels of native fish species in Berlin’s water bodies. The 2023 update (available as a brochure) builds on previous versions: the initial Berlin-wide list from 1993 (Wolter et al. 1994), as well as updates from 2003 (Wolter et al. 2003) and 2013 (Wolter & Schomaker 2013). It uses the same uniform system applied throughout Germany and the same classification criteria established by Ludwig et al. (2006) for categorising threatened species, ensuring that changes in threat levels of species can be directly compared.
The regional Red List of fish and lampreys of Berlin is rather specialised, focusing on a small and highly urbanised area. It only records and assesses fish populations in parts of the Spree-Havel system, which is somewhat of a disadvantage. However, the study of fish populations, including those of sensitive species, in these urban water bodies offers important insights into the ecological potential of highly modified environments. It helps to understand the resilience and development potential of fish species, and to identify the most effective strategies to restore these waters.
Berlin’s fish fauna comprises 50 species of lampreys and fish, of which 37 are native. Today, all three native lamprey species and five native fish species are either extinct or lost. In total, nine species are currently threatened, representing 24.3 % of the fish fauna. When including the extinct fish species, nearly half of Berlin’s original fish fauna, 45.9 % of the native species, are either lost or threatened. Additionally, the nase, an extremely rare species, has been recorded only once in the Großer Müggelsee. At present, 15 species, or 40.5 %, are not threatened.
The analysis of short-term population trends is quite concerning, as it is dominated by declining fish populations. This primarily affects species that live in small water bodies, especially the crucian carp. The weatherfish and species that favour cooler water, such as the dace, ruffe, and burbot, are also affected. The effects of climate change, which are already considerable in urban areas, are becoming increasingly palpable here.
Overall, the positive development of Berlin’s fish populations, which was attributed to the improved water quality, has come to a standstill and thus reflects the national trend (Freyhof et al. 2023). While population trends remain stable for most species, many have not yet regained their former distribution and abundance, and some are even starting to decline again. As water quality is no longer a limiting factor, targeted efforts to improve aquatic structures important to the life cycle of river fish, such as gravel spawning grounds and nursery habitats, are needed to promote fish biodiversity and restore populations.
Similarly, the overall balance compared to the 2013 Red List of fish in Berlin has deteriorated. While only six species were listed with a threat level in 2013, this number has now increased to nine. After a brief improvement in 2013, when the threat level of eleven species was downgraded from the previous list (Wolter et al. 2003), the current Red List shows only reclassifications to higher threat levels, as seen with the gudgeon, dace, and burbot. No species has been downgraded.