A unique species of freshwater pearl mussel, Margaritifera durrovensis, found only on a short stretch of the river Nore, is facing extinction unless those remaining are relocated.
A report in Irish Wildlife has described the situation of the Nore pearl mussel as desperate unless the survivors are relocated to a cleaner part of the river.
"Recent surveys suggest that there may only be 500 individuals left in total, all adult and none successfully rearing young," said the report by ecological consultant Dr Evelyn Moorkens.
She said the Nore freshwater pearl mussel was identified as a species new to science in 1928 because of the very different habitat in which the population was found.
The only known population of M durrovensis worldwide was located between Poorman's Bridge and Ballyragget, Co Kilkenny.
Ten years ago news of its imminent extinction was published, and its decline was reported to be due to depressed river bed and water quality in its habitat.
"Since that publication, numbers of Nore mussels have continued to fall. Recent surveys showed that half of the adults living in 2000 may have died by 2004. There is no evidence of juvenile survival," wrote Dr Moorkens. She said pearl mussels were the most sensitive of our protected freshwater animals requiring water quality higher than that required by humans or salmon.
They grow very slowly and live to over 100 years of age. Although they produce millions of larvae, only one in 40 million survives to become a juvenile mussel in the gravel bed of the river for a five-year period.
If the gravel in which juveniles live clogs up with silt either from drainage, erosion or decaying algae from nutrient pollution, oxygen can no longer flow freely and juvenile mussels quickly die before becoming strong enough to withstand the flow of open water.
Efforts to save the population will require keeping the existing survivors alive in the short-term and to rehabilitate its habitat conditions in the long-term.
"German workers suggest that finding a new home for them in the Nore catchment, perhaps in a cleaner tributary, may be their only hope of survival," she wrote.
She warned however that adult mussels did not relocate well. Because the species is so unique, it is not known how it might behave especially following the release from brooding in their mother's gills to release into open water, where they hitch a ride on a trout or salmon for a winter.