Lough Swilly background

Aquaculture in Lough Swilly

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Background to the issue

Lough Swilly is a flooded river valley stretching 40 kilometres into County Donegal from the Atlantic Ocean. To its east is the Inishowen Peninsula and to the west lies the Fanad Peninsula. The Lough reaches 15 and 50 metres deep and is accessible by boats at all stages of the tide as far upstream as Letterkenny. The biggest tidal range is 3.7 metres but can be as little as 1.4 metres. The shoreline of the lough is attractive with a range of scenic landscapes including spectacular cliffs and sandy beaches. The surrounding area too is picturesque with mountains and lakes, peat bogs, saltmarsh and woodland.

Lough Swilly hosts a wide variety of wildlife including rare bird species. In summer the Arctic Tern is a visitor and, in winter, the Great Northern Diver can be found. Both Common and Grey Seals can be found in the Lough.

The Lough has been protected by the Irish State and by International bodies in a number of ways. It is named in the European Habitats and Birds Directive. It also qualifies under the Ramsar Convention on Wetlands of International Importance. Furthermore, it is designated a Natural Heritage Area under the Republic of Ireland’s Wildlife Acts, 1976 and 2000.

The aquaculture industry involves the farming of aquatic plants and animals. These are deliberately ‘planted’, grown in controlled conditions and then harvested, just as in conventional agriculture. In Ireland aquaculture is based in rural areas and is a comparatively young industry. In Lough Swilly it began only in the 1980s, but has grown steadily since then.

There are a number of species farmed in the Lough:

Shellfish such as Pacific oysters (Crassostrea gigas) and blue mussels (Mytilus edulis). Many shellfish feed by taking in water – several litres each hour – and filtering out the nutrients. Fish farms rely on the sea to provide these nutrients naturally.
- Mussels are grown on the bed of the lough. After 18 months, the mussels are large enough to harvest.

Pacific oysters spend the early part of their lives in special hatcheries because Irish sea temperatures are not high enough to allow successful spawning of this species of oyster. They are then grown in bags held above the sea bed on trestles which are accessible at low tide. It will take between two and four years for the oysters to be of a marketable size.

Finfish such as the Atlantic salmon (Salmo salar) are also cultivated. Salmon naturally spend the early part of their life in freshwater so must be grown in freshwater for up to one year. When they start to change into adult fish the following spring (smoltification), they are transferred into cages suspended at sea.

Within one or two years, they are ready to be harvested

While farming finfish such as salmon and some types of shellfish requires quite deep water, sheltered from the damaging winter storms, other shellfish such as oysters require wide flat areas exposed at low tide. The great variety of landscapes in Lough Swilly allows each of these types of aquaculture to be located in the Lough. A number of operations already exist in Lough Swilly and there are proposals to extend the number of aquaculture operations there.