Thousands of oysters which were introduced into the sea off Mumbles are continuing to fare well, the marine biologist who put them there said.

Dr Andy Woolmer sent 40,000 adult native oysters overboard and onto the seabed seven years ago to see how they would prosper, or otherwise, in an area which once sustained a large oyster industry.

Dr Woolmer said a survey last summer found there had been no mass mortalities. The evidence, he said, was that the shellfish were spawning.

“Local fishermen were finding baby oysters stuck on whelk shells, which was a really good indicator the oysters had reproduced and spawned,” he said.

Dr Woolmer said the extensive survey also found oysters off Porthcawl and an area south of Mumbles Head called White Oyster Ledge. He said it was possible that some of these could have originated from the 40,000 oyster broodstock off Mumbles, but that only genetic tests could confirm this.

Dr Woolmer said “a critical mass” of oysters would be needed in Swansea Bay before any small-scale commercial fishery could be sustained.

But the area, he said, was one of very few in the UK where a particular parasitic disease which blights oyster populations was absent.

“Swansea Bay is perfect for oyster restoration,” said Dr Woolmer.

The shellfish attach themselves to hard surfaces and filter feed algae, nutrients and suspended sediment.

Dr Woolmer said what they consumed and where they lived had a bearing on their flavour – known as merroir – similar to a wine terroir.

He said a local fishery action group in Swansea, including seasoned fisherman Barry Thomas, has been very supportive of the project.

“I don’t think we could have gone that far without them,” said Dr Woolmer.

More recently, the marine biologist has been focusing his efforts on a commercial oyster fishery he has set up in Angle Bay, Pembrokeshire.

The small-scale oyster restoration project off Mumbles has reignited interest in the shellfish, leading to annual oyster festivals.

Fisherman Mr Thomas, of West Cross, said establishing a small-scale oyster fishery in Swansea would take the pressure off other species which ended up on people’s dinner plates.

For now, he reckoned the oysters off Mumbles could potentially be used to re-stock Dr Woolmer’s Pembrokeshire venture.

“I’ve known Andy for years – he’s really stuck at it,” said Mr Thomas.

“Persistence has overcome resistance.”

There is some oyster production in the Menai Strait, North Wales, along with mussels.

Mussels are also grown on ropes in Swansea’s East Dock.

Jon Parker, secretary of industry group Aquaculture Industry Wales, said aquaculture was still a small sector.

But he felt there were opportunities for land-based production in Wales of shellfish like prawns and fish such as salmon in tanks – a process known as recirculating aquaculture.

“I don’t see why Wales can’t look at more species which could be farmed and which are consumed in the UK,” he said.