Conservation programme underway for endangered Kerry freshwater pearl mussels
(Left to right) : P. Keena, D. Bluzaite, E. de Eyto (MI), R. O’Callaghan, R. McNamara (NPWS) with the newly arrived mussels in Co. Mayo.
Recognised as one of the world's most endangered species, a conservation programme is underway to prevent freshwater pearl mussels from going extinct.
Freshwater pearl mussels (Margaritifera margaritifera) are native to Irish rivers and lakes, and are protected under the Wildlife Act 1976 and listed under the EU Habitats Directive.
In July, a consignment of 20 of these mussels was airlifted from Kerry to the Marine Institute’s Research Facility in Furnace, Co Mayo, as part of the effort to save this critically endangered species.
Freshwater pearl mussels are native to the Owenmore on the north side of the Dingle Peninsula, located in the Mount Brandon SAC and the newly created Páirc Náisiúnta na Mara.
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These new arrivals will join mussels from the Newport River (Co Mayo), the Owenea River (Co Donegal) and the Owenriff River (Co Galway) as part of the conservation breeding programme being run by the Marine Institute, in collaboration with the National Parks and Wildlife Service of the Department of Housing, Local Government and Heritage, and Moorkens & Associates.
The freshwater pearl mussel is an environmentally sensitive freshwater species, owing to its complex life cycle and habitat sensitivity. While adult mussels can live for over 100 years, young mussels spend their first five or more years buried in the riverbed, where they are highly vulnerable to changes in water quality and river conditions. Their survival therefore depends on clean, stable river habitats over many decades.
Due to these sensitivities, the mussels were transported by helicopter under carefully controlled conditions with a reduced journey time to help minimise stress.
This transfer comes at a critical time: the Owenmore population is critically endangered and declining. Surveys indicate that fewer than 800 mussels may now remain in the river, compared to approximately 3,000 recorded in 1999.
In 2010, the Department of the Environment, Heritage and Local Government warned that, without intervention, the population could disappear within decades.
Pressures affecting the freshwater pearl mussel populations include sedimentation and nutrient pollution from land-use practices, which degrade the clean, well-oxygenated riverbed habitat the mussels require.
With work underway to restore the Irish catchments, captive breeding offers an opportunity to safeguard population numbers and produce juvenile mussels that can be reintroduced back into their native river.
Captive breeding is the practice of breeding endangered or threatened species in controlled environments to preserve populations and support their eventual reintroduction into the wild.
“Captive breeding gives us a window of opportunity for very vulnerable populations of mussels, where habitat restoration will take several decades. Captive breeding works alongside habitat restoration, not instead of it.
"By preserving the genetic potential of existing populations, we can buy time for restoration efforts to work, helping to secure a future for this species that plays such a key role in our freshwater ecosystems,” explained Elvira de Eyto, a researcher and biologist at the Marine Institute.
Often described as a keystone species, freshwater pearl mussels help maintain healthy river ecosystems through their natural filtering activity. However, with many populations now reduced to a fraction of their former size, this ecological function has been greatly diminished.
Ireland's National Conservation Strategy for Freshwater Pearl Mussels recognises conservation captive breeding as an important tool for preventing the loss of severely declining populations.
Part of the lifecycle of these mussels sees the microscopic larvae, known as glochidia, attach to the gills of young salmon and trout. The larvae will remain on their host fish for up to nine months before dropping into the riverbed where they continue their development.
To support this process, breeding programmes require facilities capable of maintaining both adult mussels and healthy host fish. At Furnace, Newport, Co. Mayo, the Marine Institute operates a well-regulated freshwater salmonid rearing facility.
The programme's goal is to produce large numbers of juvenile mussels that can eventually be returned to their native rivers and supplement the reproducing population.
Since its establishment in 2020, the programme has delivered significant advances in understanding the species’ life cycles in the hatchery setting, the identification of its preferred host, and best-practice handling techniques and methods to maximise juvenile survival and production.
So far, juveniles have been successfully harvested from the 2024/2025 and 2025/2026 cohorts. The juveniles will be carefully reared under controlled conditions for up to eight years before being reintroduced into suitable river habitats, helping to restore wild populations and strengthen freshwater ecosystems for future generations.
