The Natural History of Strangford Lough

The lough has a huge variety of subtidal and intertidal habitats.

The southern entrance to Strangford Lough is a deep channel about 8km long, called the Narrows. The distance from Portaferry across the Narrows to Strangford is just 0.5km, but the currents in between are extremely strong and fast, up to 8 knots. At low tide, the northern end of Strangford Lough exposes huge expanses of sandflats, indicating that about a third of Strangford Lough is intertidal. At high tide this area is covered in shallow water.

Topography and Formation

Strangford Lough is a sea inlet, which emerged from under the melting ice-sheets of the Ice Age and is for the most part less than 10m in depth. There is a deeper Y-shaped channel, possibly an old river valley or geological fault line, up to 66 m deep, which extends from the Narrows up the central portion of the lough. The surface of the bed and the indented shore of the lough ranges from bedrock, in areas with strong currents, to fine mud in sheltered waters.

The west shore of Strangford Lough has numerous islands typical of flooded drumlin topography. The lough contains extensive areas of mudflats and sandflats, with gravel, cobble, boulder and rocky shores as one moves further south. It also has areas of saltmarsh, the most extensive being in the Comber river estuary.

The water in Strangford Lough is virtually fully saline except at the mouths of the two moderate sized rivers, the Comber and the Quoile and where several streams drain into it from the catchment of about 900km². The area itself has a mild climate, infrequent frosts and prevailing west to southwest winds, with relatively low rainfall compared with other areas of Ireland.

Conservation Importance

The lough has a huge variety of subtidal and intertidal habitats. This is important for marine invertebrates, algae and saltmarsh plants, for wintering and breeding wetland birds and for marine mammals. The enormous diversity and abundance of wildlife in Strangford Lough, with over 2000 recorded marine species, makes it tremendously important for biodiversity and it is one of a network of European conservation sites. This can be seen in the huge flocks of overwintering birds and the variety of life on its shores. The lough’s wildlife depends on complex relationships and the balance between them. For example the abundant shellfish, eelgrass and other food on the northern shores are critical for the birds that overwinter there.
A long history of scientific research has confirmed the importance of Strangford Lough to nature conservation. Studies include littoral, sub-littoral and coastal vegetation surveys as well as fieldwork carried out by staff of organisations such as the Ulster Museum, Environment and Heritage Service and Queen’s University, Belfast. Its ornithological interest was confirmed in Ireland’s Internationally important Bird Sites published by the Joint Nature Conservation Committee (JNCC). In addition, the lough is one of the most important breeding sites in Ireland for common seals, despite a decline in numbers. A small number of grey seals are also present and otters are widespread.
Coastline and Island habitats
Where sea meets land the lough is fringed by the strandline. Here large quantities of dead seaweed accumulate providing a rich habitat for sandhoppers and seaweed flies, which in turn are food for turnstones, starlings, badgers and rats. This seaweed was once used as fertiliser by farmers. Throughout the spring and summer, the strandline becomes clothed with the colourful flowers of sea aster, scurvy grass, thrift, sea campion, mayweed and sea lavender.  Saltmarsh, a rare habitat in Northern Ireland, is thinly scattered around the lough. Typically, eel grasses, samphire and saltmarsh grasses build the lower marsh, while sea plantain, lavender, thrift, sea milkwort, orache, red fescue and saltmarsh rushes form the higher marsh. Rock outcrops immediately above the shore show a profusion of black, yellow and grey lichens, zoned according to the amount of wave splash. 

A variety of soil types around the shores overlay boulders and rock. Wild thyme, stonecrops, and squills grow in thin soils and remnants of maritime heath with bell heather grow on acid soils. Lime-rich grassland occurs with bee, pyramidal and twaybalde orchids and on deeper soils, scrub forms with gorse, brambles, roses, blackthorn and elder.

The character of the islands around Strangford Lough varies considerably. Some are no more than a few square metres of pebbles and coarse grasses at high tide, but are very important for ground nesting birds such as terns. Enrichment by bird droppings on some islands leads to luxuriant growth of alexanders and nettles. At the other extreme are the larger islands with deciduous woodland, pasture, scrub, hedgerows and small ponds. Livestock are used to manage the grassland for the benefit of overwintering geese, or to encourage a sward rich in flowers such as knapweed, scabious, yarrow and sorrel. These in turn provide a nectar and food source for butterflies such as meadow browns and common blues.
Strangford Lough Management Advisory Committee
The Strangford Lough Management Advisory Committee is an independent committee appointed by the government to advise on the strategic management of Strangford Lough.

It represents local and specialist interests in the development, interpretation and adaptation of legislation. The Strangford Lough Office, based in Portaferry, facilitates the work of the committee and is its main point of contact. Members bring together expertise and experience on wide-ranging issues such as aquaculture, farming, nature conservation and tourism.

(Information provided by The Strangford Lough Office and the National Trust.)