Blog Post from Chris Wynne, Conservation Officer, North Wales Wildlife Trust

Situated on a series of small islands in the lagoon, over the last decade Cemlyn’s tern colony, and in particular the Sandwich terns, have fared remarkably well.

​The five-year (2012-2016) average breeding population for Sandwich terns is 2400 pairs with an increasing trend. There is an average mean clutch size of 1.42 and productivity estimated at 0.73 over the same period.

The success of the Sandwich tern colony is remarkable –the only Welsh colony, it currently stands at about 20% of the UK population and 3% of the world population. However, this has also resulted in competition for nesting space with other tern species and disturbance for the later breeding species, especially by near fledged chicks.

2017 also produced a dramatic and catastrophic break in the Sandwich tern’s breeding population with a small family of otters devastating the colony causing complete abandonment. We are currently preparing work to help us prevent a repeat of this in 2018.
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The outlook for common and Arctic terns is less rosy with the small mixed colony of 30-60 birds having a very low productivity (0.02 or thereabouts) in recent years. In addition, there is still a notable absence of roseate terns breeding at Cemlyn and although in 2015 a pair may have “possibly” bred – based on observations of behaviour - no confirmed nest was found. The importance of restoring and boosting the common tern colony to attract breeding roseate terns to a site is well established. 

Overall, the colony faces numerous threats; with predation from large gulls and mammals being the short-term cause while in the longer-term, climate change could reduce the availability of safe breeding habitat.  The predicted increase in frequency and strength of winter storms could result in a breach to the shingle ridge at Cemlyn (which currently protect the tern islands) and as a consequence increase the risk of  
the colony flooding.
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The additional threat posed by the new nuclear power station at Wylfa, the main site for which is approximately a km away, is also substantial. Of particular relevance is the proposed breakwater at Porth y Pistyll which could lead to changes in coastal geomorphological process in Cemlyn, including accelerating and/or altering the movement of shingle.

​The Core Management Plan for the Cemlyn Special Protected Area (SPA)/Special Area of Conservation (SAC) identifies the need to provide adequate space and type of habitat on the islands to support the breeding colony – space for nests and normal bird behaviour. Over the decades, the Wildlife Trust has carried out a range of management activities to do this – including creating the western island from excavated material (late 1970’s), excavated a channel around the main islands to restrict access by people (late 1970s) and most relevant filled in a section of the main island to create further nesting space (1997)

During Summer 2017, and thanks to the Roseate Tern LIFE project, we were able to install 4 tern rafts. Although only used in a cursory way in the first year, we will be hoping for more interest from the terns in 2018. 

More significantly, in the early winter, the Wildlife Trust got to work on increasing the availability of nesting habitat on the main island. 

The main island is relatively small (0.4 ha) and includes a low-lying area of 0.05 ha i.e. c 12% of the island which is some 15-20 cm below the rest of the islands. This means, it is inundated for parts of the year and critically not available for nesting terns. Instead, loafing terns and a small number of feeding waders use it throughout the year. 

​To rectify this situation and make the area habitable for nesting tens, we proposed to import varying sized, clean small rock to raise the profile of the low-lying area. Taking material from the shingle ridge itself was definitely not on! The final landform would include small channels similar to elsewhere on the islands and a low-lying area of about ¼ of the existing one will remain. Attention was also paid to biosecurity and pollution control measures.
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However, the tern colony does not occupy Cemlyn in isolation – the lagoon, shingle ridge are a SAC, and consideration needs to made in the management of the tern colony to not impact their key features. For the former, wide ranges of specialist brackish water invertebrates are present on or in the lagoon substrate. 

To cover the area (0.05 ha) and to raise it to the right level approximately 46 tons of material was imported via the gangway onto the island.
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The opportunity provided by the gangway and transport was made good use of.  Sea beet on the island has increased considerably over the last decade and effectively occupies nesting space and provides cover for predators. We removed approximately 30% of bushes from some of the traditional common/Arctic tern areas on the east side of the island. This is in an attempt to favour these species nesting in this area. 

Through the summer of 2018, we will watching the use of the newly created areas by terns. We will also be keeping an eye on the presence of waders in the remaining low-lying areas and for any long-term impact on the lagoon.

Today's guest blog is by Lizzy Green and the Sandeel literature review she has been working on:

"I’m a Species and Habitats Officer on the Roseate Tern Life Project in the Nature Recovery Unit and have been working with the RSPB since January 2017.

The main objective of my role is to improve our understanding of tern diets around the British Isles by gathering and synthesising information from the peer-reviewed and grey literature. This involves collating information on what terns are eating, how this varies spatially, temporally and between species, and how this variation in diet affects tern breeding success. I am also analysing the impacts of diet on tern productivity using a long-term data set of Arctic tern chick provisioning from two sites on Anglesey. However, another crucial aspect of my role is gathering ecological information about key prey species for terns, such as the lesser sandeel (Ammodytes marinus).

The lesser sandeel is one of the most important prey species for seabirds around the UK, providing a high-lipid food source that, due to its long, thin body shape, is easy for chicks to swallow. However, the availability of sandeels fluctuates between years and can have severe impacts on seabird breeding success, particularly for populations with little or no access to alternative prey. Further, adult sandeels demonstrate limited dispersal ability and high habitat specificity, rendering this species vulnerable to local depletion and climate-driven reductions in their zooplankton prey.

In this literature review I collate information on the ecology, status, and distribution of the lesser sandeel, consider the drivers of inter-annual variation in populations, summarise evidence demonstrating the importance of the species for seabirds and discuss the current and potential impacts of climate change, fisheries and other factors on sandeel populations."

Today we have a blog post from Alison Brown, Roseate Tern Community Engagement Officer about the breeding terns and the hard working efforts of NWWT and volunteers at Cemlyn Bay in Wales.

You’ve probably seen the film and know the central theme that ‘if you build it, they will come’. One of the core aims of the Roseate Tern LIFE Project is for its partners to undertake enhanced management and to provide the conditions needed for a re-expansion of roseate terns in the UK and Republic of Ireland. For the Project’s participating sites where rosie’s still visit and breed; increasing their numbers and resilience presents many challenges. 

For sites recently abandoned by breeding roseate terns and where even sightings of the birds are few and far between, there is an increased urgency for pro-active management, habitat building and lateral thinking. At its’ Cemlyn Reserve, North Wales Wildlife Trust are building on a long tradition of active management and are providing new opportunities for terns to flourish and for the ‘rosies’ to come back to ‘mainland’ Wales.

Located on the north coast of Anglesey and on the eastern shores of the Irish Sea, Cemlyn is treasured for its remarkable scenery, its spectacular wildlife and its’ easy accessibility. It is this ease of access and popularity with all kinds of visitors that makes Cemlyn unique amongst all the sites being managed as part of the Roseate Tern LIFE Project. Surrounded by busy farms and farmland, the Cemlyn Reserve includes a large lagoon, separated from the sea by a spectacular, naturally-created shingle ridge. To the immediate east, the view is dominated by the Wylfa nuclear complex- currently the focus of proposals for a second nuclear power station. 

The easy accessibility of the Cemlyn Reserve, its’ lagoon, islands and nesting terns is not restricted to human visitors. The fields, wetland and scrub that surround the Reserve provide a rich mosaic of habitat for many wildlife species, including mammal predators which cross the shallow waters of the lagoon to reach the tern colonies on their low lying islands. Several species of raptors are also regularly seen in the locality and the larger gulls are also daily visitors. 

The Cemlyn Estate and farms are owned by the National Trust however, the lagoon and shingle ridge are managed by the North Wales Wildlife Trust who manage the Reserve and provide a summer warden service to help reduce disturbance, undertake monitoring and practical management as well as engaging with the visiting public.  Community engagement and supporting a wardening service at such an accessible and popular site is essential in protecting the interests of Cemlyn’s natural heritage.

While Cemlyn's shingle ridge in its' current form is geomorphologically young, being thrown up in storm 'events', the lagoon behind the shingle was effectively created in the twentieth century. Cemlyn holds a rather special place in the history of conservation, given that it was one of the first places to benefit from pro-active management solely for the benefit of its birds. The site's history as a wildlife site is tied to the story of Captain Vivian Hewitt, who came to northern Anglesey in the 1930s, settling in Bryn Aber, now a large house that dominates the western end of the Cemlyn Reserve. A wealthy eccentric, Cpt Hewitt's passion for birds led him to construct a dam and weir at Cemlyn, which replaced the tidal saltmarsh with a large and permanent lagoon intended as a refuge for wildfowl. His legacy and the creation of a stable body of water with small islands provide Cemlyn's terns with their nesting sites and a positive tradition of management that the North Wales Wildlife Trust continue today.

Maintaining Cemlyn’s lagoon islands and creating ‘space’ for breeding terns has presented a number of other challenges, not least being the ‘tension’ between overlapping European nature conservation ‘designations’.  Cemlyn’s shingle ridge and lagoon are designated as an SAC (Special Area of Conservation) and the lagoon itself is a priority feature, providing habitat for a number of rare species including the bryozoan Conopeum seurati, the lagoon cockle Cerastoderma glaucum, and the lagoonal mud-snail Ventrosia ventrosa.

Merely raising or expanding the lagoon islands for the benefit of the terns and other breeding birds is not a simple option given the potential for adverse effects on the SAC’s features of interest.  However, Cemlyn and the surrounding seas and coasts of Anglesey are also included within the Anglesey terns potential Special Protection Area and NWWT, as managers of the Site, must also maintain and ensure the integrity of Cemlyn’s ternery.

Despite these management tensions and with help from the Roseate Tern LIFE Project, North Wales Wildlife Trust have decided to continue Cemlyn’s tradition of pro-active management and to continue positive action to improve the resilience of Cemlyn’s terns by providing ‘rafts’ on the lagoon. These rafts replicate the terns’ shingle nesting habitat and provide a safer place for chicks and parents alike -protecting them from predators, disturbance and changing water levels.  The rafts are constructed from recycled plastic with a gravel tray on the top and light enough to be easily moved.  Vertical supports and cross members prevent gravel from moving around in choppy conditions on the lagoon and to deter predators, tall sides of clear polycarbonate have been added.  To avoid the rafts being used by Cemlyn’s gulls and other less welcome ‘early’ birds, NWWT staff won’t anchor the rafts on the lagoon until just before the return of the common and Arctic terns.  The use of the rafts will be monitored through 2017 with help from the team of volunteers who support the wardens.

In the first instance, the rafts are designed to help create new and safer habitat for common and Arctic terns.  However, by helping these species, and particularly the common tern, NWWT hope to build the conditions needed for the return of roseate tern which often associate (occasionally intimately!), with common tern.

‘If we build it, they might come.'