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Rare freshwater pearl mussels discovered in Scottish lochs

Rare freshwater pearl mussels discovered in Scottish lochs
Rare freshwater pearl mussels discovered in Scottish lochs
“While Scotland is a strong hold for the species, we are losing them at a significant rate. They mostly live in fast flowing highland rivers, with only a handful of rivers now known to have living colonies. So finding them in a new habitat, in our lochs, means there is more we have to learn”

Critically-endangered freshwater pearl mussels are known to live in Scotland’s rivers, but new research supported by The James Hutton Institute has revealed that they are also in our lochs.

Using remotely-operated underwater drones and snorkelling equipment, a small number of pearl mussels were discovered in two lochs in Sutherland and the Trossachs. The survey was carried out by NatureScot and funded by the Scottish Government’s Central Research Fund.

The discovery, made by using underwater drones, means conservation management for these rare creatures will be extended to lochs as well as rivers.

The mussels are likely to have entered the lochs by clinging to the gills of a host fish, either a young trout or salmon. They spend the first year of their lives harmlessly attached to the fish, before falling off to live independently.

Freshwater pearl mussels are rare in Scotland, mainly due to ongoing, illegal pearl fishing, poor water quality and habitat damage. The mussel’s over-exploitation for centuries, and the intensification of land use, are the main reasons for the massive historic decline in its numbers and range.

As filter feeders, freshwater pearl mussels are also extremely vulnerable to water pollution and engineering work in rivers. The effects of these threats mean that, in Scotland, the species is on the brink of extinction in some rivers. NatureScot is leading efforts to conserve this important and iconic species.

Dr Susan Cooksley, a river catchment ecologist at The James Hutton Institute and scientific advisor on the project, says: “While Scotland is a strong hold for the species, we are losing them at a significant rate. They mostly live in fast flowing highland rivers, with only a handful of rivers now known to have living colonies. So finding them in a new habitat, in our lochs, means there is more we have to learn.”

NatureScot’s Iain Sime, who led the latest project, said: “Other mussel species, including the much more widespread swan and duck mussels, are known to live and breed in Scottish lochs, but up until now we’ve had no evidence to suggest that pearl mussels routinely do this too.

“This project was an exciting first step in exploring our lochs and we’re keen to do further surveys to better understand more about this critically-endangered species. We don’t yet know whether they can breed in lochs and we want to learn more about a loch pearl mussel’s relationship with their host fish.

“As a result of the research we’ll be extending our conservation management advice for freshwater pearl mussels to include lochs as well as rivers.”

It’s illegal to disturb, injure, take or kill a freshwater pearl mussel. Despite this protection, illegal pearl fishing continues.

The River Dee in Aberdeenshire is one of 19 Scottish rivers designated as a Special Area of Conservation (SAC) for freshwater pearl mussel (http://www.jncc.gov.uk).

Read more about the latest research in NatureScot Research Report 1315 - Life in our Lochs - are there freshwater pearl mussel populations in our lochs as well as our rivers?

Notes for Editors

The decline of Scottish pearl mussels was first recorded in the 18th century. This decline sped up in the 20th century, with the species becoming extinct from two Scottish rivers per year on average between 1970 and 1998 (when the mussel was granted full legal protection). Many rivers still home to the species contain only old mussels, with no signs of reproduction seen.

Freshwater pearl mussels are similar in shape to common marine mussels but grow much larger and live far longer. They can grow as large as your hand and live for more than 100 years, making them one of the longest-lived invertebrates. A mussel may very occasionally bear a pearl.

These mussels live on the beds of clean, fast-flowing rivers, where they can be buried partly of wholly in coarse sand or fine gravel. They feed by drawing in river water and ingesting fine particles of organic matter. An adult freshwater pearl mussel can filter more water in a day than an average person uses to shower. They are dark brown to black in colour.

Natural Resources Wales (NRW) recently announced plans to release freshwater pearl musselsinto Welsh rivers to attempt to save them from extinction. The programme follows nearly 20 years of working out how to breed them in hatcheries.

Press and media enquiries: 

Elaine Maslin, Media Officer, The James Hutton Institute elaine.maslin@hutton.ac.uk, tel: +44 (0)1224 395076 or +44 (0)7977 805808 


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The James Hutton Research Institute is the result of the merger in April 2011 of MLURI and SCRI. This merger formed a new powerhouse for research into food, land use, and climate change.