Challenges to Improve Fish and Fisheries in Urban Waters, the Example
Berlin, Germany
Urban waters are typically characterized by higher nutrient and temperature loads, degraded and monotonous habitat structures, and further impacted by multiple stakeholders. Therefore, fisheries management is commonly restricted to fish stocking only. However, especially the most heavily degraded urban waters provide opportunities to improve fish diversity and fisheries very efficiently by improving habitat structures at comparably low costs and efforts. This is shown using the urban waters of Berlin as an example. The urban waters of Berlin, Germany, comprise and area of about 57 kmē. These waters are shared by 38000 recreational fishermen, 18 commercial fisheries with a total of 234 fishing rights, more than 25000 motor boats, inland navigation, drinking water supply, recreation and several industries, theoretically using every drop of water 2.3 times for cooling etc. In the Berlinean waters fish recruitment has been comparatively studied to identify sites and measures to improve fish spawning in 2005 with the aim to derive management suggestions for a sustainable improvement of urban fisheries. However, most serious impacts resulted from innocents. For example, at single sites more than 24000 fish eggs per mē were found, but the hatching success was limited due to arbitrary flow regulations. Wave breakers to mitigate the well known impacts of navigation-induced currents on fish fry failed because of aesthetic reasons, and so on. Accordingly, the institutional regulatory environment remained most important for the improvement of fisheries and fisheries management in urban waters.