The freshwater pearl mussel (Margaritifera margaritifera) is a large, long-lived, bivalve mollusc found in clean, fast-flowing rivers. It is a highly threatened animal, categorised as Critically Endangered within Ireland and across Europe. There are many factors involved as to why it is so endangered. The freshwater pearl mussel is listed in Annex II of the EU Habitats Directive and requires the designation of Special Areas of Conservation for its protection. The freshwater pearl mussel has an unusual life-cycle, in that the larval stage must attach to fish gills for a period of around 10 months. In Irish rivers, young Atlantic salmon are the usual hosts.
Because of this dependency, the habitats of the freshwater pearl mussel and juvenile salmonids frequently overlap. All of these species are associated with good and high water quality. While the freshwater pearl mussel requires the highest standards of water quality, works by Inland Fisheries Ireland to improve water quality for salmonids are very much to the benefit of the species.
In-stream interventions for fish conservation or angling purposes, such as rock-armouring, weir construction or the introduction of artificial spawning habitats, have the potential to negatively impact on the freshwater pearl mussel, where those structures are in, or upstream of, beds of mussels. To avoid such negative impacts, close cooperation evolved between my Department and the Central and Regional Fishery Boards, both among the organisations’ scientific staff and also at local management level. However, our understanding of the complex interactions that impact on water quality are evolving and active engagement continues between my Department and Inland Fisheries Ireland, for example in the soon to be completed freshwater pearl mussel InterReg project in Donegal.
In general, the future survival of the freshwater pearl mussel in Ireland requires close cooperation with many public authorities and other stakeholders to ensure that water quality within our rivers can support healthy populations. My Department is working with these stakeholders to achieve these aims.
