TWO thousand farmed brown trout and twenty thousand fry have been released into upland and lowland streams by scientists from The Game Conservancy Trust in order to investigate whether the many thousands of farmed fish released into our rivers each year might be having an impact on the wild population.
The project has been prompted by concerns that commercial fish stocking in some waters may pose a risk to the abundance and viability of the native wild fish populations.
Ravi Chatterji, one of the project scientists, said: “No definitive large-scale studies of this kind have been conducted in the UK before, despite the fact that many rivers have been stocked with farmed trout for at least 100 years.  

“Our study aims to provide scientifically-backed data to guide future recommendations on appropriate stocking densities of farmed brown trout in line with the conservation of wild trout populations.”
This unique project, which will run for two years, will take place on six lowland chalk streams, including the Avon, Bourne, Wylye, Allen, Frome and Piddle and two upland rain-fed rivers, the Arrow and Honddu.  
It was felt important to differentiate between the upland and lowland rivers because whilst chalk streams are characteristic of many of the famous and productive trout rivers, especially in the South of England, the majority of trout fisheries in the UK occur on upland rain-fed rivers.
Prior to starting, base-line data were collected to determine the number of wild fish in each of the project sites. The rivers were electro-fished and the wild trout were then weighed, measured and tagged, enabling the scientists to monitor any changes in growth rates during the study period.
This spring, the Trust’s scientists released a specially-calculated number of stocked fish into the study areas based on percentages of the wild population.  
Prior to release details of the fish including weight and length were recorded and an individually coded tag was placed in the membrane behind the eye.
At specific times during the study, the sites will be electro-fished to see if there has been a change in the number of stocked or wild trout present and to identify whether the growth of the wild population has been influenced by increased competition.  
Ravi Chatterji said: “It is anticipated that the results of this study will identify environmentally acceptable stocking levels, which will be economically sustainable for trout fisheries.”
The project is being run by The Game Conservancy Trust and King’s College, London and is partly sponsored by the Wild Trout Trust and the British Trout Farmers Restocking Association.