Abstract:Siltation of spawning gravels in upland rivers appears to be an increasing hindrance to salmonids' spawning success. River managers seek an eective and non-labour intensive means of loosening gravel and reducing ®ne material, so improving spawning success; this study compared three practical gravel cleaning techniques, applied at realistic (rather than intensive) levels, by assessing survival to hatching of buried brown trout, Salmo trutta L., ova at ®ve sites on four rivers with gravel substrate in southern England. Each site consisted of six reaches, of which three were cleaned by tractor rotovating, high pressure jet washing and pump washing; these were compared with adjacent, untreated reaches. Brown trout ova were buried in both ®ne mesh and coarse mesh boxes in each reach.Signi®cant improvements (at P 5 0Á05) in survival (number of live alevins) were found in three of the ®ve pump washed reaches, two of the ®ve tractor rotovated reaches and one pressure washed reach when the data were analysed by site. When data from all ®ve sites were analysed together, all treated reaches showed a signi®cant improvement (at P 5 0Á05) in egg survival to hatching compared with control reaches for ®ne mesh egg boxes; for coarse mesh boxes only pump washed reaches showed such an improvement.We feel that pump-washing provides the most eective, inexpensive and suitably non labour-intensive means of improving gravel, although ultimately it may be better to reduce the silt load of rivers. Freeze core bed samples taken before and immediately after cleaning were analysed for silt content; pump washing and high pressure washing may have reduced the amount of ®ne material.
Freshwater fish populations in England and Wales form an important resource with up to 2.2 million anglers involved in the recreational fishery. The resource consists principally of indigenous and naturalised cyprinids, and strongholds of species endangered elsewhere in Europe. Each component is under pressure from a range of sources including water abstraction and climate change. Water resources are under significant pressure and droughts in parts of England and Wales exposed the fragility of water supply systems. Climate change is a major concern, driving a re‐assessment of water supply yields. There are no objective methods available to predict changes in fish communities likely to arise from different water resource management options, except for simple systems. It is difficult to manage water resources using anything other than a precautionary approach. Accurate assessment of environmental requirements are required to strike the right balance between the needs of aquatic ecosystems and of economic efficiency.
The general understanding of how habitats influence populations of freshwater fishes in Great Britain is reviewed briefly as a component of a Europe-wide comparison. Great Britain, an island of temperate climate in the north west of Europe comprising the countries England, Scotland and Wales, has diverse aquatic habitats but a relatively impoverished freshwater fish fauna. Recreational rod-and-line fisheries for certain salmonids and non-salmonids termed coarse fish are valuable components of the economies of the countries comprising Great Britain. In some cases, distribution and abundance of fish species and their population sizes are constrained by habitat degradation. There is a growing awareness of the multidimensional importance of habitat management to develop and maintain high quality fisheries. Current knowledge of fish habitat requirements is patchy; progress has been made on salmonids and some coarse fish species. Fish habitat science has an important role in integrated river catchment management, which is reflected in recent national and international legislation.
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