Twenty of Ireland’s rarest freshwater pearl mussels were last month airlifted from a river in Co Kerry to the Marine Institute’s Research Facility in Furnace, Co Mayo as part of the effort to save this critically endangered species.

Their native river is the Owenmore on the north side of the Dingle Peninsula, located in the Mount Brandon SAC and the newly created Páirc Náisiúnta na Mara.

These new arrivals will join mussels from the Newport River in Co Mayo, the Owenea River in Co Donegal and the Owenriff River in 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.

Captive breeding offers an opportunity to safeguard the freshwater pearl mussel

Because of their sensitivity, the mussels were transported under carefully controlled conditions with a reduced journey time, helping to 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 DEHLG warned that, without intervention, the population could disappear within decades.

The pressures affecting freshwater pearl mussel populations are sedimentation and nutrient pollution from upstream land-use practices, which degrade clean, well-oxygenated riverbed habitat.

While work to restore the Irish catchments proceeds, captive breeding offers an opportunity to safeguard the freshwater pearl mussel populations and produce juvenile mussels that can be reintroduced into their native river in years to come.

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.

Often described as a keystone species, freshwater pearl mussels help maintain healthy river ecosystems through their natural filtering activity

“Captive breeding gives us a window of opportunity for very vulnerable populations of mussels, where habitat restoration will take several decades,” said Elvira de Eyto of the Marine Institute. “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.”

Freshwater pearl mussels (Margaritifera margaritifera) are native to Irish rivers and lakes and are recognised as one of the world’s most endangered species. They are protected under the Wildlife Act 1976 and are listed under the EU Habitats Directive.

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.

One of the most remarkable stages in the mussel’s life cycle occurs when microscopic larvae, known as glochidia, attach temporarily to the gills of young salmon and trout. The larvae remain on their host fish for up to nine months before dropping into the riverbed gravel, where they continue their development.

To support this process, breeding programmes require facilities capable of maintaining both adult mussels and healthy host fish.

Freshwater pearl mussels are native to Irish rivers and lakes and are recognised as one of the world’s most endangered species

At Furnace, 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’ lifecycles 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. These achievements have enabled researchers to refine breeding and rearing methods and move closer to establishing a consistent, scalable approach to freshwater pearl mussel conservation.

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.