A Case Study of the European Mudminnow Conservation Pilot Programme (2008-): Creation of surrogate habitats and self-sustaining populations, risks of climate change

The European Mudminnow Conservation Pilot Programme, initiated in 2008, is a long-term, complex, adaptive project designed to respond to changing ecological conditions. The programme's primary aim is to conserve and enhance populations of the European mudminnow ( Umbra krameri ). The number of mudminnow habitats and the size of their populations have decreased significantly in Hungary over the past few decades. The small, isolated, and shallow waters, as well as the small fish populations, are susceptible to environmental change and human impact. Mudminnows face their most significant threats from habitat loss (e.g., drying caused by climate change), disturbance (e.g., dredging), and the spread of the invasive Amur sleeper ( Perccottus glenii ). Between 2008 and 2017, we created 10 surrogate habitats (ponds) in the Szada Pilot Area, where we introduced aquatic vegetation and mudminnows rescued from 7 endangered habitats/populations in Hungary. Depending on ecological conditions, clear, turbid, shaded, and oxygen-poor alternative stable states developed in the ponds. Five habitats became excellent for the European mudminnow. Two of our artificially created ponds have established self-sustaining populations of mudminnows. Our monitoring results highlighted that extreme weather events driven by climate change (e.g., droughts, severe spring coolings) could rapidly degrade both natural and artificial shallow aquatic ecosystems, potentially driving them into an oxygen-poor state and significantly reducing the survival and reproductive success of the European mudminnow (Suppl. material 1). To mitigate the harmful effects of climate change, the main priorities are regular monitoring, habitat management (enhancement), rehabilitation, and ensuring the ecological water demands of habitats are met. We have recently developed the comprehensive Umbra Habitat Qualification System (UHQS), which is currently under validation. This system aims to reduce stocking risks by pre-assessing newly created surrogate habitats. UHQS will also be suitable for identifying and evaluating potential and current mudminnow habitats.