‘Freshwater pearl mussels are a keystone species in our rivers’

Almost one quarter of the entire mussel population in Ireland can be found in Munster 
‘Freshwater pearl mussels are a keystone species in our rivers’

Ecologist Pascal Sweeney holding a pearl mussel from the River Tay in Waterford which is over 100 years old. Picture: Don MacMonagle.

Co Kerry is one of the most prominent areas in the country for freshwater pearl mussels which believe it or not are a crucial indicator of water quality in the country’s rivers and lakes.

The Cara and the Blackwater River boast large populations of mussels and there are three other Special Areas of Conservation (SACs) populations throughout the county.

Between the two rivers, there are about 2.5m mussels which is about a quarter of the overall figure in Ireland.

There are also rivers in Munster where up until recently, pearl mussels thrived but their demise signals the increasing decline in the quality of the water in some parts of the region.

Declining salmon populations also form part of the mussels' life span in its habitat and that too is declining in many parts of Ireland.

Ecologist Pascal Sweeney examining the freshwater pearl mussel in the Sneem River in Co Kerry. Picture: Don MacMonagle. 
Ecologist Pascal Sweeney examining the freshwater pearl mussel in the Sneem River in Co Kerry. Picture: Don MacMonagle. 

“The pearl mussel indicates water quality; it has a really long life span - species born today will live for about 100 years,” Richard O’Callaghan, Kerry Life Mussel Project, told the Irish Examiner this week.

“A river must be very stable in terms of its nutrients, hydrology, etc, for the mussel to thrive there.

“Rivers are very dynamic and constantly changing but within the lifespan of a mussel, they remain relatively stable.

“The presence of the mussel also indicates a whole suite of plants and animals that have adapted to similar conditions.

“They are a bit like a keystone species, if you have the pearl mussel you can be fairly confident that other plants and animals associated with rivers - including the iconic salmon - will also be doing well.” 

Meanwhile, the Kerry Life Mussel Project ran from 2014-2020 with the aim of devising a plan that would sustain the freshwater pearl mussel and the livelihood of the local communities.

But, as Mr O’Callaghan added, when mussels start declining, so do other species and plants around it because their habitat is no longer available to them.

One such decline has been evident with salmon stock. However, he says there is sufficient juvenile salmon in the rivers for the freshwater pearl mussel.

“But with the pressure on the salmon population you would think that in the long term if you didn’t have salmon then you won’t have mussel recruitment,” he continued.

“The mussel can’t complete its life cycle without salmon. In some cases, they can use trout but because salmon returns to the river it was born in, the mussels in that river adapt to the salmon that occur in that river.” 

And when it comes to water quality and its decline in Munster, there are numerous factors at play.

Mr O’Callaghan says that other land uses over the years have contributed to the demise of water quality - not just farming. 

“From a catchment point of view in Kerry both farming and forestry are the two dominant pressures on water quality,” he continued.

“These sectors are quite intensive to the type of land in the Cara and Blackwater catchments.

“I think there is a misconception out there that Ireland’s waters are doing really well but they are not.

“Freshwater pearl mussels should be in every river from Donegal and all along the coastal counties right up to Co Wicklow.

“Just eight rivers in Ireland contain 80% of all the pearl mussels in Ireland - that is quite an alarming statistic.” 

Pascal Sweeney, meanwhile, is contracted by the Environmental Protection Agency (EPA) to survey Ireland’s rivers.

He specialises in freshwater ecology with a focus on protected species like the pearl mussel and the white claw crayfish.

Some of the work he does involves looking at insect life as an indicator of water quality.

One of the main concerns around the freshwater pearl mussel in Co Cork at the moment is their presence along the proposed route of the Ballyvoreen/Macroom bypass.

Mr Sweeney is keeping a close eye on developments and when the road is complete, he will be back surveying to ensure that the mussel and the ecological status of the nearby rivers have not been disturbed as a direct result of the construction.

“Because the pearl mussel is part of SACs there has been more of a focus on it over the last number of years,” he added.

Ecologist Pascal Sweeney says the freshwater pearl mussel is facing extinction if action to save the species isn't taken immediately. Picture: Don MacMonagle. 
Ecologist Pascal Sweeney says the freshwater pearl mussel is facing extinction if action to save the species isn't taken immediately. Picture: Don MacMonagle. 

“There are a lot of smaller rivers in Ireland that have freshwater pearl mussels in them but are not part of SACs - even though the mussels are protected under the Wildlife Act.

“It is a species that has been around for hundreds of millions of years and is heading for extinction if we don’t take responsibility and do something about it.

“The reason it's heading for extinction is a combination of a general decline in water quality and hydrology.” 

The ecology expert pointed to the need for each river to be looked at individually and highlighted how compared to three years ago when he last surveyed Ireland’s rivers, declining water quality is becoming more evident.

“General agricultural runoff into the rivers is becoming a problem; there is nutrient runoff and you can also have citation runoff which is silting up the beds where juvenile mussels are and they end up being smothered.

“Major construction projects that are now in the pipeline, some of which will cross the Blackwater River - which is heavily populated with mussels - are going to need to have an eye kept on them.

“Also salmon is needed for the life cycle of the pearl mussel and if it is blocked from going upstream, that will impact the mussel in a negative way.

“With regard to hydrology, water levels are dropping in some rivers.

“Forestry is contributing to this because the trees are sucking the water out of the ground.

“There are a whole plethora of different problems that can impact the pearl mussel and that is why each river has to be examined on its own merit.

"And, there is of course also an impact for salmon and trout in all of this.”

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