Native Oyster Restoration
Loch Craignish once supported a large population of native oysters but owing to human predation all but a few have gone. Native oysters are “ecosystem engineers”, filtering and cleaning water, sequestering carbon and contributing substantially to inshore biodiversity by creating reefs that become fish spawning grounds and nurseries.
In 2020, Seawilding secured a National Lottery Heritage Fund grant for a five-year project to grow up to 1 million juvenile native oysters in Loch Craignish to restore the natural beds.
Our juvenile native oysters, known as spat, are from Scottish stock and arrive from Morecambe Bay Hatchery weighing around 1 gramme. We grow them in our nursery, a series of floating cages, until they weigh approximately 12 grammes. This takes 3-4 months in the summer. At this point they’re big enough to sit on the sea-bottom and survive a degree of predation from starfish and crabs.
We conduct extensive baseline surveys around the Loch, searching for the best release sites which have good substrate, shelter and depth. Then, at a low spring tide, our community volunteers broadcast them by hand into the shallows.
By 2022, we'll have restored over 300,000 native oysters to the Loch, with 220,000 on the seabed. They grow exceptionally well, and so far, we have a survival rate on the seabed of approximately 40%.
THE HISTORY OF NATIVE OYSTERS
Once native oysters were common and the food of the masses and in the Firth of Forth, outside Edinburgh, 30 million were harvested annually in the 1800s. As a result of human predation, pollution and disease, globally, an estimated 85% of native oyster beds have disappeared. In recognition of their importance for ecosystem health, efforts are now being made to restore native oysters worldwide.
The native oyster (Ostrea edulis) is distinct from the oysters which you normally buy in fishmongers and restaurants. These are non-native Pacific oysters (Crassostrea gigas) and are grown commercially in farms. The native oyster is more slow-growing and generally a far superior beast.
"It's so empowering to restore native oysters and to know we can make a difference." Hannah, July 2020