Population structure and genetic stock identification of the Lough Corrib brown trout

Eurasian (brown) trout Salmo trutta populations are sensitive to alterations of their physical and natural environments (Elliott, 1994). The Lough Corrib catchment is renowned for its wild brown trout stock, which includes the long-lived, late maturing, piscivorous and highly prized ferox trout (Salmoferox). Over the past century, urban growth and associated discharges, arterial drainage, farming activities and agricultural run-off, introduction of alien species, among other factors, have all contributed to the alteration of the natural lake environment and, the loss and/or fragmentation of suitable spawning and nursery areas for brown trout. The lake has also been associated with an intensive hatchery stocking history, in particular between the mid-1960s and late 1970s. All of these factors, which are known to have an adverse effect on the demography and ecology of local populations, have contributed to fluctuations in brown trout productivity. Consequently, the health status, and long-term viability of trout populations spawning in the rivers comprising Lough Corrib’s catchment have been the focus of concern.

To assess the status of contemporary Lough Corrib brown trout populations, in 2006, IFI commissioned a research project to examine the patterns and levels of population structuring and genetic diversity focusing on nine major rivers, which were part of the TAM (Tourism Angling Measure) river enhancement programme. The results of this project have been reported by Massa-Galluci et al.(2010). In 2012, the IFI commissioned QUB (Fish Population Genetics Research Group) to carry out a follow-up genetic study on the Lough Corrib brown trout with the aim of confirming the results of the initial survey, and to investigate possible changes in the genetic make-up of populations as a consequence of the changing environment. This new study is based on a new large-scale biological survey of Lough Corrib and its main tributary rivers and streams. A key distinction between the Massa-Galluci et al. (2010) and the 2012 survey is that, for the latter, the exact location of each lake adult brown trout is known in detail. Another relevant distinction of the present genetic study is that opportunistic historical archived tissue material (brown trout scales collected from IFI fish surveys in1974 and between 1994 and 1998) was also available for analyses. This archived material allows for a direct assessment of putative genetic changes among L. Corrib brown trout populations over a twenty years period.

The results of this more comprehensive study are reported here.