Good whisky needs pure clean water, which partly explains why distilleries in Scotland always seem to have such scenic, loch-side backdrops. And one of the best ways to filter that water is oysters. Indeed, the European native oyster was so plentiful in Scotland that 30 million a year were harvested from oyster beds outside Edinburgh in the 1800s.
But today the species is almost extinct: populations have dropped by 85% over the past century, most likely because of overfishing from bottom trawling.
A new rewilding project part-funded by the Glenmorangie distillery plans to use native oysters a water filters, which would prevent the quality of the company’s whisky from deteriorating, but also mitigate the effects of the organic waste released into the waters of Dornoch Firth. In addition, researchers say the process could increase biodiversity in the area by 50% by the end of the decade.
The scheme would reintroduce 4 million oysters to the Dornoch Firth, on the north-east coast of Scotland, by 2030. As well as helping other species, it could treble the amount of carbon going into the seabed, say scientists working on the project in a new peer-reviewed paper.
The Dornoch Environmental Enhancement Project (Deep) is a partnership between Edinburgh’s Heriot-Watt University, the Glenmorangie distillery and the Marine Conservation Society. To predict its potential impact, Heriot-Watt researchers studied Scotland’s last remaining oyster fishery, in Loch Ryan, near Stranraer.
The fishery, which has operated since 1701, is unusual in that it uses a rotational harvest system. Different areas are fished, left to repopulate for six years, then fished again, allowing recovery.
The work allowed researchers to see how biodiversity increased over time if oysters were left undisturbed, and has been published in the peer reviewed journal, Plos One.
Naomi Kennon, the lead author and PhD researcher in restorative ecology at Heriot-Watt, says: “The findings from our research in Loch Ryan are extremely exciting, demonstrating that biodiversity will probably 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 also shown a link between increased shell material as the oyster population grows and increased biodiversity.”
Prof Bill Sanderson of Heriot-Watt says the findings were significant because while restorative oyster projects have increased in Europe over the past five years, a lack of data on intact reefs has meant that their impact on biodiversity has not been estimated.
“This is our best estimate of how biodiversity is able to increase,” he says. “These findings are significant for Deep and for the Dornoch Firth, but more broadly will help to inform the many marine conservation projects around the world.”
In the study, three plots – harvested one; two; and six years previously – were surveyed for biodiversity, oyster shell density and coverage. Biodiversity indicators were 60% higher in the plots that had been left for six years after harvesting.
Deep could provide a “business model for restoration”, Sanderson says. “Oysters provide food for us, they have biodiversity benefits and some work we covered a couple of years back shows that they treble the amount of carbon going on to the seabed, to be locked away.”
While populations of oysters in the area are so low as to be “functionally extinct”, he has found oyster shells dating back 8,000 years. The oyster bed in the Firth of Forth, near Edinburgh, was once 20 miles long by six miles wide.
“It’s shocking when you look at the scale of what’s been lost,” he says. “Oysters were a cheap source of protein and had all sorts of other benefits.”
Visitors to the Glenmorangie distillery in Dornoch won’t be sampling whisky and oysters anytime soon, however. Hamish Torrie, a company spokesperson, says the company became involved primarily to mitigate the impact of organic waste produced by the distillery.
“We put in an anaerobic digestion plant in 2017 which cleans up 95% of the organic waste. The idea of the oysters, which are filter feeders, was to clean up the other 5%,” he says. “The oysters have a job to do.”
