Orkney’s six SACs are located at:
Faray and Holm of Faray are two uninhabited islands which are situated between the larger, inhabited islands of Eday and Westray. The grey seal is the primary reason for selection of this site and the islands support a well-established grey seal breeding colony. The seals tend to be found in areas where there is easy access from the shore, and freshwater pools on the islands appear to be particularly important. Grey seals breed from September to December, the female giving birth to a single pup. At birth the pup is covered with a thick, creamy-white coat, and it must remain on land for around three weeks, being fed by its mother, until this is replaced by a grey juvenile coat.
The island of Hoy is located on the west of Scapa Flow and features a range of habitats and species which are found in no other part of Orkney. Despite their high exposure, its high sandstone vegetated sea cliffs provide ledges for birds and habitat for cliff plants, and northern Scottish species are well-represented. Further inland there are examples of dystrophic lochs and pools on blanket bogs and heathlands. These lochs and pools vary considerably in size and may have peat, sand or stone substrates. The water bodies support a limited flora which is typical of the acidic, low-nutrient habitat and includes bulbous rush. The extensive blanket bog is dominated by heather and hare’s-tail cotton-grass. Lichen-rich blanket bog is characteristic of higher parts of the site. In addition to pool systems and areas of extensive bog-moss Sphagnum cover, the site supports numerous peat mounds, a feature typical of, but local within, northern blanket bogs. The northern form of northern Atlantic wet heaths, characterised by an abundance of lichens is extensively developed on Hoy. A range of transitions to Alpine and Boreal heaths, Blanket bogs and flush mire are also found in Hoy. The site has the largest high-quality examples of Calluna vulgaris – Arctostaphylos alpinus heath in the UK and the community is unusually rich in lichens. The alpine heaths are developed on an impressive series of terraces. The western oceanic Calluna vulgaris – Racomitrium lanuginosum heath, occurring here with bearberry is also represented. On more sheltered slopes, there are well-developed transitions to alpine forms of the oceanic Calluna vulgaris – Erica cinerea heath, and to European dry heaths. Other interesting habitats on Hoy include petrifying springs with tufa formation, alkaline fens and calcareous rocky slopes with vegetation communities that colonise the cracks and fissures of rocks.
Loch of Isbister is an excellent example of a shallow, moderate-sized, naturally eutrophic loch supporting a rich flora. In the past the Loch of Isbister was more extensive, but encroachment by peripheral vegetation and peat has resulted in the development of a high-quality basin-mire complex, with excellent examples of open-water transition plant communities. Plants able to grow in the centre of the loch due to its shallow nature include stoneworts and pondweeds. The loch is rich in northern species and is the most northerly site for naturally eutrophic lakes in the UK. Otter are also present around Loch of Isbister.
Loch of Stenness in Orkney’s west mainland is the largest brackish lagoon in the UK and is of particular importance on account of its large size, stability, reduced salinity regime and northern location. The lagoon features a salinity gradient and sustains communities representing sheltered marine, brackish and freshwater conditions. Loch of Stenness is predominantly sedimentary and the floor of the basin has a covering of soft mud, while round its shoreline muddy sediments with sand and gravel grade into pebbles, cobbles and boulders. The soft sublittoral mud supports mats of filamentous green algae and large numbers of burrowing worms, and the bivalve Mya arenaria and the snail Hydrobia ulvae may be dominant. Around its shores boulders are dominated by filamentous green algae or fucoid algae, and in places Fucus ceranoides, characteristic of brackish conditions, is abundant. Submerged boulders in more saline areas of the lagoon support clumps of mussels, the brown alga Fucus serratus and species of foliose red and filamentous green algae. In the inner parts of the loch, where salinity is reduced, stands of beaked tasselweed grow.
Sanday is a large, low-lying island which is located between the islands of Stronsay, Eday and North Ronaldsay. Surrounded by clear, relatively shallow water, the island has a complex coastline dominated by extensive sandy beaches and sheltered inlets, interspersed with rocky headlands. The primary reason for selection of this site is the extensive area of sub tidal bedrock reefs that surrounds the island and provides a substrate for dense forests of kelp. The kelp occurs to a depth of about 20m and provides a habitat for species-rich, red algal turf communities. Sponges and ascidians occur on the vertical rock faces. The north coast of Sanday is tide-swept and appears to support a richer fauna than the south coast, with a dense bryozoan/hydroid turf and dense brittlestar and horse mussel beds in mixed sediment below the kelp zone. Crabs and brittlestars are common within crevices in the rock. Other habitats present around the island include sandbanks which are slightly covered by seawater all the time, and mudflats and sand-flats not covered by seawater at low tide. Sanday is also an important site for the common seal. Breeding groups of seals can be seen on intertidal haul-out sites which are distributed around the island’s coast and the near-shore kelp beds provide them with important foraging areas. Common seal pups are born during June and July and, unlike those of the grey seals, are able to swim almost immediately after birth.
This cliff site on the north Atlantic coast of Mainland Orkney is selected as an example of extremely exposed cliffs in the north of Scotland. The combination of high, hard, acidic rock cliffs and exposure to wind and salt spray results in one of the largest examples of maritime vegetated cliff in Scotland, associated with well-developed cliff-top transitions. Grazed cliff-top maritime grassland supports red fescue, thrift, spring squill and sea plantain. Further inland this grades into maritime heath, rich in species such as Scottish primrose and with an unusual maritime form of crowberry-rich heath present on deep, free-draining mineral soils, and cross-leaved heath on wetter soils. A further habitat present in this SAC is alkaline fen.