MALLTRAETH MARSH/CORS DDYGA
SITE OF SPECIAL SCIENTIFIC INTEREST
Management Statement
What is ‘special’ about Malltraeth Marsh SSSI?
Malltraeth Marsh has 8 special features:
Open water associated with the lowland grazing marsh ditch system and former river meanders with associated plants and animals such as reed canary-grass, water-plantain and branched bur-reed. Club-rush, and reed sweet-grass are also dominant in parts. Submerged plants such as spiked water-milfoil, blunt-leaved pondweed, horned pondweed and uncommon plants such as flowering-rush, water-violet and marsh stitchwort are abundant.
Pillwort – an aquatic fern
Variable dragonfly
A water beetle Hydrochus brevis
Wintering shoveler
An assemblage of breeding birds of lowland damp grassland such as lapwing, curlew, redshank and snipe.
An assemblage of breeding birds of open water such as teal, gadwall, and pochard.
Water vole
As well as the features listed above, Malltraeth Marsh has other habitats/earth science features that contribute to the special interest. These include marshy grassland, lakes, pools and trees as well as fossiliferous coal and shales on old colliery spoil heaps. This mixture of habitats is important for much of the wildlife including other dragonflies (such as the hairy dragonfly) and other invertebrates, bittern and heron. These too are key components of the special interest of the site. Unless specified below, management of this site should aim to look after these habitats and species as well as the listed features of interest.
There are two management options for Malltraeth Marsh:
The retention (and enhancement) of the current man-made grazing marsh system with its associated wet ditches, lakes and swamps, which is dependent on the long term maintenance of Malltraeth Cob and the Cefni embankments.
The restoration of the former estuarine environment of saltmarsh, natural grazing marshes and freshwater transitions in the event of the destruction or abandonment of the Malltraeth Cob or Cefni embankments.
Both options have conservation value. Only the former will be considered further at this time.
The site should support a rich aquatic flora and fauna in the artificial drainage ditches and former river meanders. All the nationally rare plants (e.g. pillwort, marsh stitchwort) and scarce Welsh plant species (e.g. flowering rush and mare’s-tail) should be present, with each in at least 3 locations within the SSSI. There should be a rich invertebrate fauna including the water beetle Hydrochus brevis, and the dragonfly assemblage should include both the variable and hairy dragonfly. Breeding birds associated with this habitat should include teal, tufted duck, shoveler, gadwall, pochard, little grebe, great crested grebe, water rail, sedge and reed warblers, mute swan and reed bunting.
Swamp, dominated by common reed, should cover at least 30ha and provide habitat suitable for breeding bittern with edges of open water for feeding.
Typical breeding birds of lowland damp grassland such as lapwing, curlew, snipe, redshank, shelduck and grasshopper warbler should be present. This assemblage should be broadly distributed across the whole site (i.e. not concentrated in one compartment or landholding).
What management is needed on Malltraeth Marsh SSSI and why?
Although Malltraeth Marsh is an excellent place for wildlife and geology it will only be 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 Malltraeth Marsh if they are not properly managed. These are the ones we regard as most important:
Water levels: Drainage ditches on the marsh were originally clay-lined to convey water from higher ground and thus retained water throughout the year. This clay was removed by mechanical excavation. Relining the ditches and/or penning summer water levels would retain summer-wet conditions in now seasonal ditches and restore the wetland flora and fauna. Such ditches would also provide farm stock with water and help control livestock.
Feeding waders require soft ground and high water levels in the fields to bring invertebrates to the surface. High water level in adjacent ditches helps to maintain soil water levels in the spring and create suitable feeding conditions for breeding birds. On sand or silt soils it can also help extend the growing season into the summer drought. Removing water from the land as quickly as possible means most fields are too dry for feeding waders by late spring. Excavation of shallow wet scrapes in large fields, especially on old river meanders, can be used to create wader feeding areas.
Construction of sluices or other water control devices where field drains meet the main drains (parallel to the Afon Cefni) and at two or more points along the main drains would allow groundwater levels to be maintained at higher levels for longer in the spring.
Ditch maintenance: Ditch cleaning is essential for the maintenance of open water but the frequency of cleaning should permit regeneration of aquatic and emergent vegetation. Ditches should be cleaned no more than once every two years and most should be cleaned every 5 years or less. Alternatively, leaving uncut sections or sides can be used to retain seed material and cover for wildlife. Care should be taken to retain clay linings by using weed cutting buckets or weed forks. Ditches should not be over-deepened (which removes clay linings where they still exist) or re-profiled with steeper sides. They should have sloping or stepped sides to allow emergent species such as flowering rush to grow. Abandoned field ditches should be reopened or re-lined to improve connections within the ditch network, making it easier for aquatic species to spread and increasing the area of available open water.
Overhanging scrub and other vegetation should be cut back (outside the nesting season) when the ditch is cleaned.
Application of fertilisers or any other materials such as creamery waste should avoid a 10 metre wide strip alongside every watercourse and ditch to avoid nutrient pollution. In the lower part of the site, which drains into the adjacent SAC a 25m strip should be left untreated.
Introduced plants: There are many introduced species of aquatic plant which have the potential to choke rivers and lakes causing the loss of species previously present. Fairy fern and Australian stonecrop, for instance, are both present on Anglesey, in garden ponds and as escapees and are very hard to control. Fairy fern is already present within the SSSI at Crochan Caffo and Paradwys. Care should be taken to sterilise equipment or machinery which may be contaminated with seeds or root fragments when moving into or out of the SSSI or between holdings. Himalayan balsam spreads rapidly along ditches as its seeds float and it is already present in the SSSI. It should be controlled wherever possible by hand-pulling and removing from site to be burnt or composted – if left to lie it is capable of rooting and growing again.
Introduced fish: Many species of fish find food by digging in lake and ditch beds; this leads to poor water quality as nutrients within the sediments are released and fine particles of mud and silt are suspended in the water. Poor water quality leads, in turn, to a loss of aquatic plants of interest either because insufficient light is reaching them or because increased nutrient levels in the water lead to a rapid growth of a small number of less desirable species. On this site there is a risk of fish escaping during flood events to colonise ditches and pools elsewhere in the marsh, no matter how well managed the fishery is. Bottom feeding non-native fish, or native fish not already present on site, should not therefore be introduced to any water body within the site.
Ground nesting birds are very vulnerable to predation. Some, such as lapwing, select large fields with wide views and nest communally to benefit from shared defence. On this site crows are major predators, attracted by carrion and by tall, neglected hedges, which provide nest sites and vantage points for spotting eggs and chicks. Regular trimming and or laying of hedges will reduce predation risk to nests. Water voles are also vulnerable to predation by mink. Vigilance is required to maintain the area free of this predator
Breeding numbers of lapwings and other waders have fallen throughout UK in recent years. The provision of suitable habitat here may not lead to an immediate increase in breeding numbers but should allow the population to build up – if similar provision is made elsewhere.
Finally
Our knowledge and understanding of wildlife is continually improving. It is possible that new 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, in particular, of the possible/probable impact of climate change. 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.
Your local office is:
Countryside Council for Wales
Llys y Bont
Ffordd y Parc
Parc Menai
Bangor
Gwynedd
LL57 4BN
Fax: 01248 679259