What is ‘special’ about Cemlyn Bay SSSI?

Cemlyn Bay has 3 special features:

As well as the features listed above, Cemlyn Bay has other habitats/earth science features that contribute to the special interest. These include the shingle barrier, saltmarsh, coastal grassland, marshy grassland, scrub, freshwater pools, ditches, inter-tidal rocks and rock pools This mixture of habitats is important for much of the wildlife including black-headed gulls, water vole, a range of wintering wildfowl, brackish water-crowfoot, beaked tasselweed, narrow leaved eelgrass, lagoon cockle Cerastoderma glaucum, lagoon mud snail Ventrosia ventrosa, lagoonal isopod Idotea chelipes, brackish-water sea mat Conopeum seurati and several species of clover, and these too are a key components of the special interest of the site. Unless specified below, management of this site should aim to look after these habitats as well as the listed features of interest.

What do we want Cemlyn Bay to look like?

The site should contribute to the breeding tern population within the Irish Sea and more locally along the coast of Anglesey. Its integrity as a breeding site for all tern species should be maintained, primarily by keeping it free from ground predators. This should occur even in years where one or more of the nesting species fails to be present. The integrity of the tern population is dependant upon off-site factors, such as availability of food, the presence of alternative nesting sites in adverse years within the Irish Sea and the integrity of their winter migration sites. The site should provide the opportunity for roseate terns to nest. As they tend to nest in established tern colonies, usually associated with common terns, the maintenance of a viable common and arctic tern colony is imperative.

The integrity of the shingle ridge and its associated flora, including sea kale, sea radish and yellow horned poppy, should be maintained along with the low salinity lagoon. The site should support wintering wildfowl including wigeon, shoveller, goldeneye, teal, mallard and tufted duck. Saltmarsh and brackish pools should be characterised by beaked tasselweed, brackish water-crowfoot and associated lagoon specialist invertebrate fauna

What management is needed on Cemlyn Bay SSSI and why?

Although Cemlyn Bay is an excellent place for wildlife/geology it will only remain so if the necessary management continues. CCW’s aim is to work with you to ensure that this management is carried out.

What does this mean in practice?

There are many factors that could damage the special features at Cemlyn Bay if they are not properly managed. These are the ones we regard as most important:

Competition for Nest Space: Expansion of the area occupied by breeding gulls has the potential to reduce the viability of the tern colony through direct occupation of nesting areas. Management of the gull colony (by removing gull nests and / or eggs within a specified exclusion area around the core tern breeding colony) may be necessary to maintain a viable tern nesting area.

Providing appropriate nest sites: Roseate terns regularly nest in holes and hollows, including nest boxes. In order to provide greater nesting opportunities for roseate terns, nest shelters may be placed within the colony prior to occupation each year.

Disturbance: Nesting terns require freedom from human disturbance. The presence of the Coastal Footpath along the shingle ridge requires sensitive visitor management. Re-routing of the footpath below the ridge crest is essential during this period, and should be pursued through the appropriate mechanisms. In the winter visitor pressures are less, but wintering wildfowl would benefit from lower levels of disturbance associated with footpath diversion.

Predator control: Nesting terns require freedom from ground predators – notably foxes and stoats. The maintenance of a deep-water channel between the single ridge and the nesting islands discourages access by ground predators. Pre-season trapping reduces the predator pressure on the colony. Wardening throughout the nesting season also assists in reducing predation from other bird species, such as gulls and peregrines and from egg collectors. Provision of nest boxes or shelters may help reduce predation of terns by other species.

Salinity: The salinity of the lagoon is crucial to the unusual brackish water fauna of the lagoon, including an isopod Idotea chlipes, found nowhere else in Wales. The salinity also maintains the saltmarsh and its characteristic flora around the lagoon’s edges. The maintenance of the subtle mix of freshwater inflow, seepage through the shingle and leakage through the weir is essential to maintaining the salinity balance within the lagoon.

Trampling: Although subject to movement during winter storms, the shingle vegetation may be susceptible to trampling pressure. Recreational use and walking should therefore avoid the vegetated areas of the shingle ridge.

Shingle supply and mobility: The shingle ridge is maintained through a dynamic and generally cyclic process of deposition and erosion of the shingle. Structures or other intervention that interfere with this natural movement should be resisted. Although the ridge consists of a large volume of shingle, the overall resource may be limited. Removal of shingle to provide building material has occurred in the past but must be resisted. Rising sea levels and storm events due to global warming make this even more important.

There are a number of off-site factors that have the potential to significantly impact on the features of this site. These factors are highlighted below:

Water quality: Changes of landuse in the catchment (e.g. intensive dairy or arable farming) have the potential to influence water quality. Sediment load, chemical (nutrient) and organic pollution could affect the water quality within the lagoon.

Food supply

Nesting terns require a regular supply of suitable fish (sandeels and other small pelagic fish) available to foraging birds within a short distance of the colony. Any actions or events likely to impinge on this resource should be resisted.

Alternative Sites

Cemlyn bay is one of a suite of sites around Anglesey and other parts of the Irish Sea (including Rockabill island and Lady’s Island Lake in Ireland), which are used by nesting terns. Former sites such as Rhoscolyn Beacon and Ynys Gorad Goch may be re-occupied in the future. Actions or events likely to affect the availability of these alternative sites should be addressed through appropriate mechanisms.

Wintering territory

Terns are migratory birds and spend most of their lives away from the nesting colony. Actions or events likely to impinge on the sustainability of the population should be addressed through appropriate mechanisms.


Our knowledge of wildlife is far from complete. It is possible that new features of value may appear and new management issues may arise in the future, whilst other issues may disappear. This statement is written with the best information we have now, but may have to change in the future as our understanding improves. Any information you can provide on the wildlife of your site, its management and its conservation would be much appreciated.

If you would like to discuss any aspect of your SSSI, or have any concerns about your SSSI, please contact your local CCW office.

Cyngor Cefn Gwlad Cymru/Countryside Council for Wales

North Region

Llys y Bont,

Ffordd y Parc,

Parc Menai,


Gwynedd, LL57 4BN,

Telephone: 01248 672500

Fax: 01248 679259