| Summary: | study was undertaken within the river Avon catchment in order to assess the factors limiting Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) densities. After summarizing current existing knowledge on salmonids and the Avon catchment, field research was focused on the physical habitat of spawning and first summer juvenile salmonids. At numerous locations throughout the catchment area visual assessments were made on water flow, surface substrate size distribution, and ability to rear salmonids. From these initial observations ten sites were selected as potential spawning and rearing areas and underwent qualitative analysis including measurements on water depth and velocities, types of available cover, and surface substrate size distribution through pebble counts. Finally, additional sediment characteristics were analysed at three sites, by performing surface embeddedness counts, and sub-surface bulk sampling. It was found that salmonids were limited in the amount of physical habitat available for spawning and juvenile rearing; while water flow, cover, and sediment were of good quality in three confirmed spawning locations, there were few areas within the Avon catchment that meet the conditions required by spawning and first summer juvenile Atlantic salmon and brown trout. This is not only a result of the Avon dam, which controls and regulates water and coarse sediment flow from the Avon headwaters, but also a consequence of land use and the natural geomorphology of the Avon catchment.
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