Brown trout swimming in a river

National Brown Trout Research Programme

Brown trout are one of very few native fish species in Ireland, and they are an important element of biodiversity in lakes and rivers. They are widespread geographically and are found in every catchment around the country. Several types of brown trout occur in Irish freshwaters, including ferox, gillaroo, sonaghan and croneen. Brown trout can be used as indicators of environmental quality because they require relatively clean water and are sensitive to pollution and habitat degradation. Their presence and abundance tell us about the quality of the waterbody that they inhabit.

Brown trout are a valuable recreational angling resource. Ireland has a wealth of large and small lakes and river systems—over 74,000 kilometres of rivers and streams and 128,000 hectares of lakes. Many of the larger lakes support excellent populations of brown trout. The Great Western Lakes of Carra, Conn, Corrib and Mask are renowned among the finest brown trout fisheries in Europe. Brown trout fisheries across the country support an estimated €148 million in annual tourism revenue.

Brown trout.

How we do our work

Inland Fisheries Ireland explores many aspects of brown trout biology and ecology. We investigate their habitats, population status, growth rates, life histories, genetics and the environmental pressures that threaten them. We use a variety of methods to collect information about brown trout, including electrofishing in rivers, survey netting and hydroacoustics in lakes, as well as radio and acoustic telemetry for exploring migratory patterns and interactions with other species. Such research helps to inform decision making by providing a strong scientific evidence base for national policy and management decisions.

Electrofishing survey for brown trout fry index in a small tributary of Lough Ennell, 2021.

What we are doing

Developments in brown trout research at Inland Fisheries Ireland include a national fry index programme, stock assessments of large lakes, genetic studies and investigations of interactions between trout and other fish species, such as pike and dace. These field studies provide data that can be used to study how trout populations behave and how they relate to other fish species.

Baseline and long-term fish sampling programmes are an important part of assessing the presence, distribution, ecology, biology and status of fish populations. Baseline monitoring characterises existing conditions and establishes a database for planning or future comparisons. Long-term monitoring involves surveys at spaced at regular intervals in time to provide information on population trends, growth rates, shifts in fish community structure, recruitment rates and the impact of environmental pressures, such as pollution.

Juvenile brown trout caught during electrofishing survey for fry index, Tudenham Stream, 2021.

Genetics studies

In 2006, Inland Fisheries Ireland began collaborative studies with university research groups to study the genetics of brown trout populations in Lough Corrib and its inflowing rivers. This research was followed by similar studies based on Lough Mask, Lough Ree, Lough Sheelin and the Boyne, Shannon and Suir river systems.

Our work on the genetics of Irish brown trout populations have enabled us to determine which inflowing rivers are the most important contributors of young fish to populations in lakes and rivers. These studies also provide information on how the genetic structuring of brown trout populations is affectd by habitat degradation, hatchery trout stocking programmes, fish kills, poor water quality and invasive species.

Brown trout spawning.