Durham University was commissioned by the Environment Agency and the Grayling Research Trust to examine the seasonal movements and habitat use of European grayling Thymallus thymallus in unregulated rivers dominated by surface flow. The aims were to: The study was carried out mainly on the River Rye catchment in North Yorkshire. Radio-tracking was undertaken on the Rye over two periods, January to July 2004 and October 2004 to January 2005, as well as habitat surveying, environmental monitoring and limited electric fishing surveys and mark–recapture. A subsidiary radio-tracking study was carried out on the River Ure, North Yorkshire, between February and April 2004.



A series of recommendations were made based upon this research. The adaptive pattern of seasonal movements by grayling in many rivers, which probably helps to enhance survival probability and sustain populations, especially in those rivers with variable flow and/or greater spatial dispersion of key habitats, needs greater consideration in river management. This study, as well as other published material, suggests that many barriers across which brown trout can gain easy access may not be easily passed by grayling. Careful assessment of the need for new obstructions, operation of existing structures and possible removal of potential barriers to movement should therefore be considered.

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