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Fish are heavily influenced by the nature of the flood regimes of the rivers in which they live. These fluctuate naturally from year to year but recently increasing pressure on water for a wide range of uses other than fisheries has led to human activities that have substantially altered the flood regimes of many rivers throughout the world. This has resulted in the loss of fish production and biodiversity. There are now efforts to mitigate for these changes that include release of artificial floods from dams or polder sluices. The typical flood curve contains several characteristics that may influence the survival and growth of the individual fish species. Understanding of these characteristics will help design appropriate flood curves and maximize benefits from the water available.
The Restoration Ecohydrology Concept integrates two approaches to restoration and mitigation of physically modified freshwater habitats. Firstly actions at the catchment level connected with integrated management of abiotic factors including, landscape planning, catchment management, forestation, phytotechnologies and hydrology by impoundment. Secondly actions at the level of the aquatic ecosystem itself, particularly those linked to fisheries management. The highest biodiversity and productivity of fish assemblages appears at an intermediate level of human disturbances, which, in the case of the biogeochemical cycle, has usually been connected with limited degradation of catchment cover. The increase of fish biomass and diversity under these conditions apparently results firstly from nutrient enrichment and improved energy influxes to the stream arising from the more rapid cycling of nutrients of terrestrial origin cycling, and secondly from the intermediate complexity of the riparian ecotones. The maximum of biomass might appear under different conditions than those that favour maximum biodiversity due to this ecosystem enrichment and amplified access to energy. The data presented at the symposium lead to following conclusions: 1. Restoration of river systems to pristine conditions is not realistic but is also not necessary. 2. The target of restoration of physically degraded habitats should lie somewhere in the range between maximum biodiversity and maximum productivity of fish communities.
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