The unique partnership that is bringing back Scottish oysters

On the banks of the Glenmorangie Distillery in Scotland’s Dornoch Firth, where oysters were overfished to extinction a century ago, an ambitious restoration collaboration by a business, a university and a marine conservation society has been going on for almost a decade.

Begun in 2014 as part of the distillery’s wider sustainability strategy, the Dornoch Environmental Enhancement Project (DEEP) aims to introduce four million European native oysters by 2030 into the protected area of the Dornoch Firth, next to the distillery.

After archaeological research showed that oysters had existed in the area for 10,000 years, scientists tested the waters for survivability. In 2017, the scientists took 300 oysters from the UK’s only sizable wild oyster population in Loch Ryan and carefully placed them in two experimental sites in Dornoch firth. More than 80% of the experimental oysters survived. 

In October 2018, waste shell from the scallop and mussel industry were used to cover the seabed in two locations to form the first pair of a series of reefs, mimicking the conditions in which they would have grown before they became extinct. Between October and the spring of 2019, they placed 20,000 oysters, grown by suppliers across the UK, on the reefs.

Sylvia Duckworth, Wikimedia

The scientists aim to create a self-sustaining oyster population. In October 2022, another 6,000 native oysters were introduced to the Dornoch Firth, taking the total deployed so far to over 40,000. The project will reach a total of 60,000 oysters in the Firth by the end of 2022.

As well as restoring long-lost oyster reefs to the marine protected area of the Dornoch Firth, the project is intended to enhance biodiversity and, along with Glenmorangie’s newly commissioned anaerobic digestion plant, help purify the waters of the Firth. And now new research in Scotland’s oldest still functioning oyster fishery confirms that it can do both.

The oyster survivability trials coincided with the official opening in 2017 of the €6million anaerobic digestion plant at Glenmorangie’s Tain Distillery. The plant is expected to purify up to 98% of the waste water that the distillery releases into the Firth with the remaining 2% of the organic waste accounted for by the filter feeding of the oysters.

The plant can treat up to 2,500 cubic metres – the equivalent of eight days of the remains of the barley. The reactor produces high quality water which is returned to the firth, a copper-rich sludge that will assist local barley farmers who rely on fertilizers for copper-deficient land, and bio-gas that creates steam that will help power the distillery, reducing reliance on fossil fuels by 15%. 

Within ten years, established oyster reefs will comfortably soak up this remaining 5% because they ingest plankton and other matter, build organics and nutrients into their tissues and lock away sediments on the seabed.

Now research by Edinburgh’s Heriot Watt University at Scotland’s last remaining native oyster fishery at Loch Ryan in Dumfries and Galloway has confirmed that increasing the shell material in waters increases the number of species that are present. Their findings, outlined in a paper published in the scientific journal PLOS ONE, are significant for DEEP, says Heriot-Watt professor Bill Sanderson.

The Loch Ryan fishery has operated since 1701 and uses a rotational harvest system, with  different areas being fished each year and left to repopulate for six years before they are fished again.

Naomi Kennon of Heriot-Watt, said the findings “demonstrate that biodiversity will likely double over a decade once oyster restoration projects are complete. This means the population of species will increase in a balanced way. Our data has shown a link between increased shell material as the oyster population grows and increased biodiversity.”

The Marine Conservation Society also was delighted. “The Loch Ryan study shows that increasing the complexity of the seabed allows many species to find refuge in this living reef,” said Calum Duncan. “We look forward to thousands more native oysters being released in the Dornoch Firth, to attract even more biodiversity.”

But it won’t happen overnight. “Putting oysters back into a system like the Dornoch Firth will take time (and appropriate licences) because the habitats will need time to mature and oyster populations will require a concerted effort to boost them back to a realistic size,” says Bill Sanderson in the Conversation. “This means long-term thinking and commitment, which happily comes naturally to a company whose products takes a minimum of ten years to produce.”

“For now, the DEEP project has recovered a forgotten past where oyster beds were once plentiful, and made possible a future where the return of oysters to the east Highland coastline means sustaining a healthy marine environment in a natural way,” he says.

DEEP is one of a series of projects aimed at returning native oysters around the UK.

Sources:

Oysters galore! How whisky is helping to bring back native molluscs to the Scottish Highlands. The Conversation, May 23, 2017

Loch Ryan study ‘significant’ for Dornoch Firth oyster reef restoration project. Northern Times, Apr. 6, 2023

Dornoch Environmental Enhancement Project (DEEP). Native Oyster Network UK & Ireland.

Images by Native Oyster Network UK & Ireland