Why Scotland's oysters are losing their claim as the food of love

Outside in the dark of night, women oyster sellers lugged huge baskets packed with fresh oysters across the cobbled streets to sell to leering drunks and gentry alike.

From the Firth of Forth where native oysters were extracted in incredible quantities and oyster gangs from Fisherrow, Prestonpans and Musselburgh battled to control the trade, to coastal towns and cities around the country, oysters were the perfect 19th century fast food to be guzzled like today’s barflies might throw back a packet of peanuts.

There seemed be no end to the supply: it’s estimated around 30 million were taken from the Firth of Forth alone each year.

By the time calls came for more sensible harvesting in the 19th century, it was too little and too late.

Now efforts to restore native oysters to a handful of carefully selected waters have met the kinds of perplexing problems that could benefit from the brilliant minds of the Scottish Enlightenment.

The latest – and one which could potentially derail efforts to restore some west coast native oyster sites – hinges around the food of love’s apparent inability to breed.

For although oysters are considered as an aphrodisiac to get the juices flowing, they have turned out to be the giant pandas of the underwater world when it comes to doing what comes naturally.

At Loch Craignish, the sea loch between Oban and the Crinan Canal that opens onto the Sound of Jura, where bottom trawling, dredging and pollution combined to decimate oyster numbers, efforts began in 2020 to revive native oyster reefs.  

Using finger-nail size oysters bred at a specialist hatchery in England and then lovingly nurtured at the loch’s floating nursery, the hope was to restore one million native oysters to the loch.

The largest project of its kind in the UK, so far it has placed 350,000 on the seabed, of which around 90,000 are believed to have survived predatory crabs and star fish.

On the plus side, Seawilding Scotland say they have found small, juvenile oysters attached to boat hulls and nursery cages, suggesting the newly restored population is now reproducing.

But plans to grow a further 300,000 oysters in its nursery to release on the seabed have been dramatically hindered by a lack of oyster love action at the UK hatchery that supplies their stocks.

“A bit like giant pandas you can give them all the love in the world, but they won't necessarily oblige,” confirmed Seawilding Scotland.

It means that its Craignish project, its similar effort at Loch Broom and every other UK project relying on a new stock of native oyster ‘babies’ for their seabed restoration plans, have been without a supply for over 12 months.

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To make matters worse, an outbreak of disease last year at the main hatchery supplying native oyster spat, saw its entire brood stock lost.

Adding to the woes, sea temperatures across the North Atlantic rose last year, making Loch Craignish 3˚c warmer than normal. That impacted plankton on which the nursery oysters feed and raised fears of higher mortality.

Then, for any youngsters which do make it the waters of Craignish, is a further problem: an exceptionally high number of starfish only too keen to gobble them up.

All of which has required enlightened thinking, with Seawilding Scotland now attempting to use miniscule oyster larvae harvested from the loch’s existing stocks – each roughly the width of a human hair – to grow in their nursery.

First, of course, they have to catch the microscopic strands, using a technique has never been tried before in the UK.

It has all added up to challenging times for the country’s largest oyster restoration project and raised worrying questions over what the future might hold.

Could it fail? “Potentially,” concedes Danny Renton, Seawilding Scotland’s CEO, “but there are many reasons why projects can fail; lack of supply is one, lack of funding is another.

“We’re still optimistic we can follow through and recover from this. We are hanging on in there.

“We are being inventive and trying to find out other ways of sourcing supplies.

“With these projects,” he adds, “half is about restoration on the ground and the other half is about research, so we are concentrating on research.

“And our core activity of putting down hundreds of thousands of oysters is currently on hold.”

The attempt to ‘catch’ larvae in the loch and nurture it in its nursery is groundbreaking for the UK and there are no guarantees it will work.

But, adds Dan, it’s worth a try.

“In France, in areas where there are millions of youngsters, they put coupelles, l8ft long sticks covered in lime, in the water,” he explains.

“The larvae float around and as they look for things to grow on, they attach to the lime.

“They grow for a few months and then we put them in areas where we want to unlock the population.

“We know it works elsewhere, but no one has done it in the UK.”

Around 150 lime-covered cages with mussel and scallop shells attached for the larvae to attach to, have been suspended at key points on the loch. Adult oysters are carefully positioned in the hope they will release chemical cues to encourage the free-floating larvae to settle.

If successful, the ‘spat-on-shell’ will be transferred to the project’s nursery cages and seabed restoration sites.

But, adds Dan: “Restoration is a numbers’ game. You have to put in millions and millions.

“Putting 10,000 or 20,000 down is not really meaningful, they are very slow growing, and predation is really high from crabs and starfish.”

Loch Ryan native oysters will be celebrated at Stranraer Oyster Festival in September (Image: Colin Hattersley)

One solution might be to import supplies of native oysters from European hatcheries where there is a plentiful supply.

But rules surrounding importing live shellfish and a host of other issues mean that is off the table at least for several years, he adds.

“Unless we can solve the supply issue with existing hatcheries… well, you can imagine the problem we have,” he adds.

There is some exasperation. Restoring oysters and the group’s other focus, seagrass, fit perfectly with government agencies’ aims for marine biodiversity enhancement: oysters act as a natural water filter, cleaning pollution and supporting a range of other species.  

While Danny points to New York’s Billion Oyster Project which has received a wealth of government support in its effort to seed New York Harbor with 1bn oysters by 2035.

“We don’t seem to have ambition in Scotland,” he adds. “Whilst authorities are encouraging this as part of biodiversity strategies, there is not the funding or ambition or regulatory framework to really expand it.

“We would like some investment to help hatcheries or to get a new hatchery going to ensure continuation of supply.”

With no fresh supplies of spat likely until September at the earliest, the project has concentrated on research. One strand has used hydrodynamic modelling of Craignish to better understand the movement of oyster larvae and where best to focus restoration efforts.

That might help tackle a project which, concededs Danny, was “always going to be a struggle.”

“We are dealing with a marine space that is massively compromised in terms of diversity and an ecosystem that is no longer there.

“So much has gone, and we are trying to put back one component and expecting it to survive.

“It’s a wonderful idea, but we are learning it is very complex.”

Loch Craignish is just one of a number of native oyster restoration projects now underway in Scotland.

Efforts began in 2017 to restore oyster reefs in the Dornoch Firth, in a project involving distillers Glenmorangie, Heriot-Watt University and the Marine Conservation Society. By the end of 2022, around 60,000 oysters had been returned to the waters.

While Restoration Forth aims to restore four hectares of seagrass and 30,000 oysters to the Firth of Forth by the end of this year.

At Lochaline Harbour in the Sound of Mull, another project involving Seawilding Scotland, up to 20,000 native oysters are being grown in suspended cages beneath the floating pontoons waiting to be released.

The organisation has also been looking at a similar restoration project at Loch Gair, near Lochgilphead.

But oysters are under additional pressures as seas become more polluted with the tiniest contaminants.

Last week scientists at the universities of Portsmouth and Brighton found “disturbing” levels of tiny glass fibre particles widely used to make small boats in mussels and oysters for the first time.

And researchers at the University of Barcelona have found as much as 85% of mussels and 53% of oysters they examined had ingested microplastics.

Here, a small handful of reefs which once supplied the nation’s voracious appetite for oysters remain: Loch Ryan’s native oyster beds are among the most important of their kind in Europe and protected by a Royal Charter presented by King William III in 1701.

With oysters on the OSPAR List of Threatened and/or Declining Species and Habitats, the harvest of 20 tonnes per year is carefully managed so only the largest are taken.

In mid-September, the produce will be celebrated in a throwback to the days of the Oyster Club, oyster howffs and oyster street sellers of the past at Stranraer Oyster Festival, a three-day celebration of the last wild native oyster fishery in Scotland.

Native oysters being opened at Stranraer Oyster Festival 2022 (Image: Colin Hattersley)

There’ll be cookery demonstrations, a line-up of celebrity chefs, an oyster bar and The Scottish Shucking Championship.

Scotland’s native oysters - once commonplace, enjoyed by the rich and poor alike and now a rare delicacy - will once again take centre stage.

For more about Stranraer Oyster Festival visit www.stranraeroysterfestival.com