Pearl fishing was once a widespread activity in Ireland. In fact, pearls have been found in rivers throughout the country, and they have been a feature of Ireland's past since the ancient Irish began to trade pearls with the Phoenicians in exchange for the secrets of producing purple dye.
Throughout the centuries, pearl fishing in Ireland has ranged between a casual occupation and an organized commercial concern. The fisheries that were established on most major rivers never reached national importance, since only one in ten thousand freshwater mussels contains a valuable jewel. Nevertheless, the pearl has been used in Ireland for personal and religious adornment, and has made an impression on Irish folklore, legend and art. It even appears in some Irish stories to signify the patriotic homeland, which produces such a pure and precious gem.
The price of pearls has varied greatly depending on when, where and to whom they were sold. It is the poor who have fished Ireland’s rivers for pearls and the pearls affected the social conditions of those who fished for them.
John Lucey, a biologist with the EPA, and a historian wrote The Irish Pearl. This book traces the place of the Irish pearl in the myth, history, commerce, science, arts and literature of Ireland. It draws on gemmology, biology and economics as well as on historical and literary resources to shed light on a hitherto neglected aspect of Irish history and culture.
So, that is what I have on my brain today, St. Patrick's Day! I must admit that this above section was shamelessly copied from Lucey's book introduction listed here.
I also read an Irish Naturalist Journal April, 1947 article in which Arthur Went offers numerous accounts of the discovery of pearls throughout Irish rivers from mid 1500s to the 1900s. Irish freshwater pearls were considered the most valuable pearls, even more highly regarded than saltwater pearls. Mussels were fished for in the hopes of discovering pearls as well as utilizing the mother-of-pearl in the shells. Fishing for these mussels ceased when the cultured pearl industry made a strong showing in the 1900s.