摘要
Most of the river systems in the British Isles have been subjected to anthropogenic influence to varying degrees over recent times, in many instances leading to deleterious impacts on salmonid habitat to the detriment of populations. This paper considers the range of management options that can be utilised to overcome habitat degradation. When examining salmonid habitat management three areas need to be taken into account: water quality, water quantity and the physical structure of the riverine environment. Although discussed separately, it should be remembered that these components of habitat are inter-related, and should be viewed as a continuum. Water quality problems include pollution from point and non-point source pollutants, although major improvements in the former have been achieved in recent years via the legislative framework and further benefits may be anticipated from the introduction of the Water Framework Directive. However, diffuse forms of pollutant, notably silt, still remain a significant threat to salmonid habitat and are yet to be tackled in any meaningful way. Changes to modern agricultural and land management practices are urgently required. Water quantity is impacted upon in a number of ways ranging from abstraction, which may reduce flows, through to land-use and flood defence that may alter the shape of the hydrograph changing velocities and influencing stream power. Society’s conflicting demands are bound to increase these pressures, although imaginative and integrated planning of schemes can avoid many deleterious impacts and actually provide benefits to salmonid populations, provided the ecological requirements of the species are taken into account. Arguably a more flexible and targeted approach to river regulation and abstraction would be beneficial to salmonid populations. Degradation of physical stream habitat has been widespread caused primarily by insensitive land-use practices, agriculture and flood defence. A significant commitment to consider long-term investment of resources will be required to negate the widespread deterioration in habitat caused by such damaging management techniques. Although a wide range of physical habitat restoration techniques have been demonstrated both in-stream and within the riparian zone with significant success, it is suggested that some form of land-use regulation is required to prevent further damage. Treating the root cause of the problems of deterioration with respect to water quality, quantity and physical habitat, and not just the symptoms, should be a fundamental priority for salmonid management in the 21st century.