Natural regenerations of endangered fish populations in the Pilica drainage basin after reducing human impacts

Summary

In the Pilica River drainage basin the impact of pollution, overfishing and engineering was largely responsible for detrimental limitations in fisheries. Stopping sewage inflow into the Pilica River and its tributaries due to the construction of a man-made reservoir supplying drinking water in the middle course of the river, caused a natural regeneration of many populations, including the appearance of fish in a river section in which fish were formerly completely absent. The main long term stress is overfishing caused by anglers and poachers, because both these groups are still abundant and take all captured fish away for human consumption or feeding animals. Engineering, which consists here in protecting eroded banks by reveting them with fascine or limestone boulders, is unfavourable for fish only in the initial phase and more in small than in large rivers. Revetments provide many hiding places for fish and make net operation for poachers more difficult, but they are quickly damaged by water flow.