Freshwater Pearl Mussel
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What to look for:
Freshwater pearl mussels need water of the highest quality in a river or stream where either trout or salmon also live. This is essential for the lifecycle of the freshwater mussel.
Male mussels disperse their sperm in the water, the fertilised eggs develop inside the female mussel and over 2 million minute larvae, looking like minute mussels, are released by the female during the late summer. Thousands of young mussels are free living for a short time but most die because in order to successfully develop the larvae must be inhaled by a young salmon or trout.
Once inhaled the young mussels must attach themselves to the inside of the gill to survive. The miniature mussel closes on the gill fan where it hangs growing in the highly oxygenated environment. They do no damage to the fish and drop off the following summer hopefully sinking onto a suitable sand or gravel bed where they grow to adulthood over the next twelve years.
When to see it:The freshwater pearl mussel is a protected species throughout its range in Scotland therefore you must not wilfully disturb or touch it. During the early summer when water levels are low, oystercatchers that have travelled inland to breed sometimes find and feed on the pearl mussels leaving the empty shells on the riverbank.
Where to see it:This mussel is a highly threatened species which is only found in fast flowing, non-alkaline rivers and streams, where the beds have course sand and gravel into which they can bury.
Things to think about:
An adult mussel can live for more than 100 years. Freshwater pearl mussels were once common in the clean Scottish rivers and streams, over-fishing and pollution have destroyed most stocks. Current research is developing methods for mussels to propagate in salmon and trout fisheries to provide stocks to seed new mussel beds in protected rivers.
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