Freshwater Pearl Mussel Glochidia Found in SW Scotland!


31st Oct 2019
by Beth de Lacy

Last week GFT were out electrofishing on a tributary of the River Bladnoch surveying four different sites.

The photograph shows glochidia on the gills of a trout parr.
The photograph shows glochidia on the gills of a trout parr.

The burn is known to have one of the last remaining populations of freshwater pearl mussels (Margaritifera margaritifera) in South West Scotland.

The survey was to check salmon and trout numbers and to check for the presence of mussel glochidia on the parr.  It is exciting to be able to report finding glochidia on the gills of trout parr. Glochidia are the larvae of freshwater pearl mussels which are released through summer and attach themselves onto the gills of passing salmonid parr. This is a great sign as it suggests that the pearl mussels are reproducing.

It is thought that certain temperatures cause female freshwater pearl mussels to release up to 4 million glochidia, most of which will perish. A small number however, will successfully attach onto passing parr and stay there until the following summer where they then drop off into the river bed and continue to develop. Freshwater pearl mussels can live to be over 100 years old making them one of the longest-lived invertebrates. They have been subject to a large amount of poaching across Scotland over many years making them now highly protected. It was great news finding glochidia in some of the trout and salmon parr!

 

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