Pearl mussels
The luminous pearls which attracted Julius Ceaser to Britain are now dangerously rare.
Pearl mussels are among our oldest river inhabitants and were once found up and down the country. Sadly, commercial exploitation and industrial pollution have pushed populations to the brink of extinction. Pearl mussels are now scarce everywhere except for a small number of Highland rivers
The freshwater pearl mussel has been fished in Britain since pre-Roman times and Scottish pearls were first traded in Europe as far back as the 12th Century. In the 1700s, commercial use reached such a peak that river bailiffs were employed across Britain and Ireland to ensure that valuable pearls were kept for the King. This wide-scale exploitation only halted in 1998 when the pearl mussel was afforded complete legal protection.
One of the longest-living invertebrates known, the pearl mussel survives on average for around 100 years. Breeding season begins in early summer when the males shed sperm into the water to be inhaled by females. Fertilised eggs are then released in the form of tiny larvae which (if lucky) attach themselves to the gills of host fish where they live and grow until the following spring. The young mussels then drop off, hopefully into a clean gravel or sand bed, where they settle down for the next stage of their life cycle.
Pearl Mussels do not mature until they reach 10-15 years of age. Until that time, most juveniles live completely immersed in the sand bed. Mussels can re-bury themselves if dislodged, and are also capable of moving slowly across sandy sediments. Upon reaching maturity, most adults live with approximately a third of their shells exposed.
Facts
Appearance: Unlike saltwater mussels, the pearl mussel shell is long and oval - like an elongated clam shell. The colour is usually dark brown or black
Size: Between 7cm and 15cm
Lifespan: 80 - 120 years
Diet: Pearl mussels inhale water through exposed siphons and filter out minute organic particles on which they feed
Family: Mollusc
Did you know?
- Sea trout, brown trout and Atlantic salmon are the only native host species in Europe
- Therefore, changes in levels of salmon and sea trout may affect mussel populations
- It is still legal to sell mussel pearls that were caught prior to the 1998 ruling
- The Kellie pearl, found in an Aberdeenshire river in 1621, forms part of the Scottish crown jewels
- Small mussel populations still survive in a handful of English rivers, including the Torridge (Devon) and the North Tyne
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