PEARLY GATES Cal
With the number of common oysters falling dramatically, Cal Flyn looks at some of the conservation work that is bringing endangered reefs back from the brink
Flyn investigates the conservation work helping save the native oyster
What do you think of when you think of oysters? Lemon slices and tabasco sauce? Cocktail dresses and Champagne? Oysters are a luxury item these days, and priced accordingly, but not so very long ago they were cheap as chips – and as plentiful as potatoes.
In 1868, the author Robert Chambers described an oyster cellar scene not unlike the late night kebab shops of today: parties of fashionable types ‘would adjourn in carriages to one of those abysses of darkness and comfort, called in Edinburgh laigh shops’, he wrote, ‘where they proceeded to regale themselves with raw oysters and porter, arranged in huge dishes upon a coarse table, in a dingy room, lighted by tallow
candles. The rudeness of the feast, and the vulgarity of the circumstances under which it took place, seem to have given a zest to its enjoyment.’
Once very widespread, overfishing during the 19th century saw the populations of Scotland’s vast stocks of native oysters plummet. At its peak, one of the biggest fisheries in the Firth of Forth produced 30 million oysters a year, but by 1920 numbers had collapsed to the extent that fishing ceased. By 1957 oysters were locally extinct, and the same pattern unfolded along much of Scotland’s coastline.
The common oyster is now, unfortunately, rare. Indeed, oyster reefs are amongst the most endangered marine habitats on the planet. Today they are most likely to be found along the more remote parts of Scotland: Shetland and the Hebrides, plus in Galloway’s Loch Ryan, the site of Scotland’s last remaining wild oyster fishery.
Native or common oysters live densely in vast ‘beds’ or reefs in shallow seawater, anywhere from the low tide line to 80m in depth, where their shells provide a solid surface for lots of other ocean life like seaweeds, sea slugs and sea squirts to live on. And though they may seem like simple creatures
“Robert Chambers described an oyster cellar scene not unlike the late night kebab shops of today
– two shells, a muscle clamping them shut – you may be surprised by how fascinating the lives that they lead really are.
For one thing, they are all born male, but after 18 months to two years become female. Over the course of their six- to 15-year lifespan they may alternate back and forth between the sexes. They too show complex biological rhythms: not only attuned to the circadian clock (day versus night), and the tidal clock (high versus low) but to the lunar cycle. Scientists at the University of Bordeaux showed recently that the molluscs’ degree of opening was linked to the phases of the moon – not only the levels of moonlight, but whether the moon was waxing or waning – and posited that they have evolved an internal lunar clock much like our own internal 24-hour clock.
They too serve a key ecological role. As filter feeders, they strain plankton and other particulates from the seawater – processing up to 30 gallons a day – and it is this function that has inspired a cutting-edge environmental project in the Dornoch Firth.
In 2017, a team from Heriot-Watt University, in partnership with the whisky company Glenmorangie and the Marine Conservation Society, embarked upon an ambitious plan to reintroduce the common oyster to the waters off Tain, restoring its lost oyster beds. After a successful pilot project involving 300 oysters – the ‘canaries in the cage’, according to Dr Bill Sanderson, an associate professor of marine biodiversity at the university – the team began the enormous task of installing 20,000 more on two artificial reefs last autumn.
At the moment, if one was to dive down you would see ‘mounds of consolidated shell with oysters amongst it’, Sanderson explains. ‘Over the summer this will become colonised with other invertebrates, seaweeds and fish. We are expecting to see a biodiversity hotspot by the end of the year.’
As Hamish Torrie, director of corporate social responsibility at Glenmorangie, explained at the project’s launch: ‘This restoration of oyster reefs will help us realise our long term vision of a distillery in complete harmony with its natural surroundings.’
The company’s new anaerobic digestion plant in Tain purifies around 95% of the organic waste from the effluent produced by the distillation process, before it is released into the Dornoch Firth. The final 5% is then expected to be naturally filtered out by the oysters.
Long term, the aim is to install a selfsustaining population of four million oysters. This is roughly equal to the original oyster population of the firth 250 years ago, and represents a full restoration of the long lost reefs. ‘The Dornoch Firth is a marine protected area with conservation legislation that prevents extraction of oysters from the site,’ says Sanderson. ‘The oysters are therefore not for eating. We are hopeful, however, that once the population gets established, larvae will spill out into the wider Moray Firth and we will start to see fishable populations out there.’
It’s not the only initiative of its kind. Over on the west coast a community group called Cromach (Craignish Restoration of Marine and Coastal Habitats) has been taking matters into
“Over the course of their lifespan they may alternate back and forth between the sexes
its own hands. ‘The people who live here had been sidelined when it came to the use of their shoreline and inshore coastal waters,’ explains Cromach’s Rory Day. ‘Over the last few decades this has often meant watching helplessly as wild fish numbers dwindle, local waters are polluted, and the seabed and the species that live there are damaged or destroyed.’
Set up to promote effective marine management, the group now has 100 local members and in May this year it acted to reintroduce a thousand juvenile oysters, each roughly the size of a two pence piece, into the waters of Loch Craignish. ‘We put them in cages with shelves – a bit like a wire chest of drawers, giving them protection from predators but enough room to move with the tide,’ says Day.
‘We weighted down the cages and dropped them very gently onto an intertidal rock and shell bed by the edge of a seagrass meadow in the loch. There were about a dozen of us, children included. It was very exciting.’
Pupils from nearby Ardfern Primary will assist in monitoring the oysters’ development, and should they do well, there are plans to expand the scheme. ‘Maybe they’ll spawn soon if all the conditions are right,’ says Sanderson. ‘We don’t know if or how they’ll spread, but apparently the larvae freeswim for over two weeks – in a best case scenario they might end up as far south as Crinan, across the other side of the loch or even round the other side of the peninsula in Craobh Haven and into the Sound of Jura.
‘A thousand settled oysters could spawn hundreds of thousands more,’ he adds. ‘But equally, we may have to start all over again in just a few months. If it all goes well, the bigger oysters will get released every three years or so.’
The costs of reintroducing this first batch was supported through grant funding from the conservation charity Sea-Changers and donations in kind from Barcaldine’s Lochnell Oysters just north of Oban. (For more information, or to volunteer your time or expertise, visit cromach.org.)
With luck, plus some muscular efforts from conservationists, we can hope that Scotland’s oyster population will rebound— and with it, the health of our marine ecosystems.