Native oysters are being introduced into the waters around Scotland for the first time in more than 100 years.
The European flat became extinct in most areas around the coast in the 18th Century due to overfishing.
Varieties of mainly non-native molluscs are currently farmed around the country for the food industry.
But now a team from Heriot-Watt University has returned 300 natives to the Dornoch Firth as part of a water-purifcation project.
If the oysters survive, the plan is to create a reef covering four hectares.
On their first inspection, the university team have seen a 90% survival rate which they say is encouraging.
The oysters perform a valuable function in marine life by filtering the water that passes through them.
Dr Bill Sanderson is one of the scientists working on the scheme, which is believed to be the only one of its kind in the UK.
He says restoring the mollusc population will take time.
Dr Sanderson said: "The aim is about four hectares of oyster reef at a density of about 10 per square metre.
"To achieve that, we will have to put quite a lot of oysters in here and we have to grow them first.
"So there is a bit of work ahead to do this."
The project is being funded by the Glenmorangie distillery which pumps cleaned waste water into the firth.
Hamish Torrie, the company's director of corporate social responsibility, said: "Oysters are biofiltration geniuses. They can really clean up the water and are perfect for marine life.
"Basically, they will store carbon and that sort of thing so they are hugely important for the eco-system of the sea."