Upsurge in coarse fish stock endangers trout
Native brown trout are in a minority on Lough Corrib – and vastly outnumbered by invasive coarse fish – according to new research from Inland Fisheries Ireland.
The IFI's recently published fish stock survey for Ireland's second largest lake reveals that just over two per cent of the fish surveyed were brown trout.
The study, conducted in 2024 and published in February 2026, showed the vast majority of fish surveyed were coarse and non-native invasive species.
On upper Lough Corrib, just 20 of the 994 fish surveyed were brown trout. On the lower lake, just 22 of the 765 fish surveyed were brown trout.
Despite the low numbers of trout recorded, IFI's own report hails Lough Corrib as being ‘regarded as one of the best game fisheries in the world’. “The brown trout fishery, which is of considerable economic and cultural importance is internationally renowned,” the report adds.
Mike Donnellan of Oughterard Anglers Association said IFI's figures confirm about 93% of fish in the lake are non-native, predatory and invasive.
“How can they call it a brown trout fishery of considerable economic and cultural importance and internationally renowned when their own figures show that it is in effect a coarse and pike fishery?” he asked.
Mr Donnellan said the figures were damaging to trout tourism because anglers coming from England, France and Germany “can no longer assume that they will catch brown trout in the Corrib”.
He said that the IFI was conserving pike and coarse fish on the lake through bye-laws 806 and 809 that safeguard non-native, predatory and invasive species.
Both bye-laws, he argued, are repugnant to the EU Habitats Directive which defines the “conservation status of a natural habitat” as the sum of influences acting on it and its typical species, affecting long-term distribution, structure and survival.
Fish protested under 806 and 809 are not “typical species” he said, and should not be conserved.
Mr Donnellan said IFI's solution to the problem is to try to introduce 'catch and release' and reduce the allowable catch on the Corrib for trout anglers.
But he insisted that solution ignored the problem of non-native fish, such as roach and perch, which he said should be removed from the lake.
Mr Donnellan pointed to Kylemore Lough in Connemara and Doo Lough near Delphi in Mayo, which had relatively higher populations of brown trout.
“That's because they don’t have invasive species,” he said.
The IFI survey of Kylemore found 85 trout, and the survey on Doo Lough found 94.
No pike or perch were found in either of these water systems. “The number of non-native fish species present is inversely proportional,” said Mr Donnellan.
On lower Lough Corrib, roughly south of Knockferry at Moycullen, 765 fish were recorded in the survey, and 84% of them were perch (249) and roach (396).
North of Knockferry, in the Upper Lake, 610 perch were detected representing 61% of the 994 fish recorded. The next most populous species was roach with 190.
A total of 86 roach and perch hybrids were discovered in Lough Corrib, more than the total number of brown trout, which numbered just 42.