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Seas off St Kilda SPA

Status: Special Protection Area (SPA)

The Seas off St Kilda SPA covers the waters around the St Kilda archipelago, more than 50 km west of North Uist in the Outer Hebrides.  In spring and summer, this part of the Atlantic Ocean teems with more than 600,000 pairs of seabirds, most of which breed on St Kilda.


The Seas off St Kilda SPA is close to the continental shelf edge where the seabed drops sharply from a depth of about 100 m in the east of the area to more than 400 m in the north-west. The shelf edge is a zone of high productivity of fish and other small marine organisms. The concentration of these prey items makes these waters important feeding grounds for seabirds. In 2014, the shelf edge to the north-west of St Kilda was classified as a Marine Protected Area (Geikie Slide and Hebridean Slope Nature Conservation MPA) for its benthic habitats.

More than 7% of Britain’s breeding gannet population exploits the Seas off St Kilda, capturing mackerel, herring, sandeel, and other fish for themselves and their young. Not only do gannets feed here – other iconic St Kilda seabirds such as fulmars, puffins, and the nocturnal storm-petrels occur in large numbers. The seabirds of St Kilda comprise one of the largest and most spectacular marine seabird community in western Europe and one of the most important in the whole North Atlantic.

Seabirds breeding on St Kilda are protected on land and in the waters immediately surrounding the colony by the existing St Kilda SPA. Although capable of flying hundreds of kilometres, gannets nesting on St Kilda feed mostly in the productive and readily accessible waters around the islands. The Seas off St Kilda SPA complements the protection at the colony and ensures that the marine foraging area and the prey on which the seabirds depend are also protected.

More detailed site information can be found in the Summary section below.


Map displaying the Seas off St Kilda SPA boundary. Visit JNCC's MPA Mapper to further view and explore data for this SPA.



Legislation behind the designation: The Seas off St Kilda marine Special Protection Area was classified by the UK Government to meet obligations set out in the Birds Directive (2009/147/EC), and is protected by The Conservation of Offshore Marine Habitats and Species Regulations 2017 (as amended). Other regulations apply in inshore waters.


Protected Features

Feature Feature type % population Conservation Objective
northern gannet Morrus bassanus (breeding) Migratory 7.63% GB
(5.2% biogeographic)1,2
assemblage of breeding seabirds Migratory [N/A; >20,000 birds] Maintain
northern fulmar Fulmarus glacialis (breeding) Migratory 0.22% GB2
(but >2,000 ind)
European storm-petrel Hydrobates pelagicus (breeding) Annex I 1.24% GB2 Maintain
common guillemot Uria aalge (breeding) Migratory 0.11% GB2
(but >2,000 ind)
Atlantic puffin Fratercula arctica (breeding) Migratory 0.36% GB2
(but >2,000 ind)

1 Biogeographic population size was added where species qualified based on this under Stage 1.2 of the Site Selection Guidelines.

2 To be a named component of a seabird assemblage a species needs to be present with at least 1% of it’s GB population, or with >2,000 individuals.

Note that the wording is in accordance with the conservation objectives, drafted to provide information during the public consultation. See also the Conservation Advice section.


Conservation Objectives

The overarching conservation objectives for the protected features of this site are to ensure they either remain in or reach favourable condition. The ability of a designated feature to remain in or reach favourable condition can be affected by its sensitivity to pressures associated with activities taking place within or in close proximity to a protected site.

Specific information on the conservation objectives relating to this SPA is provided in the Conservation Advice section.


Site Timeline

The diagram below is a summary of the key milestones involved in the selection and classification of the Seas off St Kilda SPA.

October 2016
Public consultation. Site becomes a proposed SPA.
December 2018
Site formally recommended to government as a SPA.
December 2020
Site classified as a SPA.


Relevant Documentation

The documents referred to below and any other historical documents relating to the Seas off St Kilda SPA were produced during the selection and classification process and therefore may be out of date. This Site Information Centre is the most up-to-date source of information for this SPA and will reflect any additional information gathered since these documents were produced.

Information about the general UK SPA site selection process is available on the SPA webpage. More detailed information about the selection of marine SPAs in the UK can be found on the Identification of marine SPAs webpage.



Last updated: September 2020

Site overview

The Seas off St Kilda SPA is located in Scottish marine waters about 50 km north-west of North Uist in the Western Isles of Scotland. It covers 3,995 km2 of mainly offshore waters and encloses the St Kilda archipelago, consisting of the four islands of Hirta, Dun, Soay and Boreray, and the sea-stacks of Stac an Armin, Stac Lee and Levenish.

In the site, water depths range mainly between 40 m and 410 m, and the bathymetry shows that this site lies very close to the continental shelf edge, with water depth quickly increasing to the west and to the north of its limits. Shelf-break fronts are a typical phenomenon at the shelf edge and, like almost all fronts, are regions of enhanced plankton production, leading to a higher fish production. Shelf edges might also have a function in concentrating marine organisms both in acting as a barrier to species confined to shallower waters, and as a feature guiding the migration of fish.

The combined effect of current and waves creates low-energy seabed environments in most of the site. In the vicinity of the archipelago, however, moderate-energy seabed environments also occur. In the south-west of the site, rock and reef habitats are prevalent; the north-west is dominated by a mosaic of subtidal coarse sediments and sand and muddy sand habitats.

Like most of the continental shelf edge, Seas off St Kilda is a nursery ground of mackerel Scomber scombrus. Northern gannets typically have a highly varied fish diet and common species consumed in UK waters include mackerel Scomber scombrus, sandeel Ammodytes marinus, sprat Sprattus sprattus and herring Clupea harengus.

Seabird population estimates and important usage areas for seabirds in the Seas of St Kilda SPA are based on data from the European Seabirds at Sea database (ESAS) collected between 1980 and 2006. The analysis of ESAS data indicates that the SPA holds the largest regularly occurring marine aggregation of breeding northern gannet identified in UK waters; it is the only area where this species occurs regularly in numbers greater than 1% of its biogeographic population. Northern gannet therefore meets the Stage 1.2 SPA selection guidelines for migratory species. All other qualifying species occur with > 1% of their GB population (European storm-petrel), or with > 2,000 individuals (all other species) in the site and qualify as parts of the breeding assemblages under Stage 1.3 of the guidelines.

Further detail on the evidence for this SPA can be found in the Evidence section.

Site location: the boundary of this SPA can be viewed on the map, which also includes the boundary co-ordinates.

Site area: c. 3,995 km2.

Site depth range: At Seas off St Kilda, water depths range mainly between 40 m and 410 m; shallow areas with less than 100 m depth occur only at the very east of the site, while depths of more than 250 m are reached only in the north-west.

Site boundary description: The seaward boundary of the Seas off St Kilda SPA is based on the extent of the important aggregation of northern gannet. The landward boundary is adjacent to the existing St Kilda SPA. The SPA extends into offshore waters beyond 12 nautical miles; hence it is a site for which both NatureScot and JNCC have responsibility to provide statutory advice.

Information for this site summary was adapted from documents listed in the Relevant documentation section.



Last updated: April 2018

Site-specific data

Data were requested from the European Seabirds at Sea Partnership and analysed by JNCC.

The full overview of how these data were used to support site identification, along with information on confidence in the protected features occurrence and abundance is available in the SPA Site Selection Document.


Survey and data gathering

  • ESAS data (1986–2006) – The European Seabirds at Sea (ESAS) database is the most comprehensive and longest running dataset for the distribution of seabirds at sea in north-west European waters. Boat-based transect data from 1980–2006 were extracted and analysed to identify distribution hotspots of seabirds throughout the year. Further details on the methods and survey coverage are available in JNCC Reports 431 and 461.


Data analysis reports

Additional relevant literature

Please be aware that although these sources contain information which is of interest in relation to this SPA, they do not necessarily represent the views of JNCC.

  • Begg, G.S. & Reid, J.B. 1997. Spatial variation in seabird density at a shallow sea tidal mixing front in the Irish Sea. ICES Journal of Marine Science: Journal du Conseil, 54, 552–565.
  • Camphuysen, K.J., Fox, A.D., Leopold, M.F. & Petersen, I.K. 2004. Towards standardised seabirds at sea census techniques in connection with environmental impact assessments for offshore wind farms in the U.K.: a comparison of ship and aerial sampling methods for marine birds, and their applicability to offshore wind farm assessments, NIOZ report to COWRIE, Texel, 37 pp.
  • Coull, K.A., Johnstone, R. & Rogers, S.I. 1998. Fisheries Sensitivity Maps in British Waters. UKOOA Ltd.
  • Ellis, H.I., Milligan, S.P., Readdy, L., Taylor, N. & Brown, M.J. 2012. Spawning and nursery grounds of selected fish species in UK waters. Science Series Technical Report No. 147. CEFAS, Lowestoft, UK.
  • Hamer, K.C., Phillips, R.A., Wanless, S., Harris, M.P. & Wood, A.G. 2000. Foraging ranges, diets and feeding locations of gannets Morus bassanus in the North Sea: evidence from satellite telemetry. Marine Ecology Progress Series, 200, 257–264.
  • Mann, K.H. & Lazier, J.R.N. 1991. Dynamics of Marine Ecosystems: Biological-Physical Interactions in the Oceans. Blackwell Scientific Publications: Oxford.
  • McBreen, F., Askew, N., Cameron, A., Connor, D., Ellwood, H. & Carter, A. 2011. UKSeaMap 2010: Predictive mapping of seabed habitats in UK waters. JNCC Report No. 446.
  • Nelson, B. 2002. The Atlantic Northern Gannet. Fenix, Great Yarmouth.
  • JNCC generic documents, 2016:
  • Stroud, D.A., Chambers, D., Cook, S., Buxton, N., Fraser, B., Clement, P., Lewis, P., McLean, I., Baker, H. & Whitehead, S. (eds). 2001. The UK SPA network: its scope and content. JNCC, Peterborough.


Knowledge gaps

If you are aware of any additional data or relevant scientific papers for this site not listed in the relevant documentation please contact us.


Conservation Advice

Last updated: September 2020

Conservation Objectives

Conservation objectives set out the desired state for the protected feature(s) of an SPA. The conservation objectives for the protected features of the Seas off St Kilda SPA are set based on knowledge of the condition of the protected features at the time of writing. Any future updates of the conservation objectives for this site will be published here when available.

This information is useful if you are:

  • Preparing Habitats Regulations Assessments (HRAs) of proposed plans or projects that may affect the site;
  • Planning measures to maintain or restore the site and its qualifying features;
  • Monitoring the condition of the qualifying features; or
  • Developing, proposing or assessing an activity, plan or project that may affect the site.

Until the updated conservation objectives are available, the following preliminary conservation objectives have been drafted by JNCC:


To avoid significant deterioration of the habitats of the qualifying species or significant disturbance to the qualifying species, subject to natural change, thus ensuring that the integrity of the site is maintained in the long term and makes an appropriate contribution to achieving the aims of the Birds Directive for each of the qualifying species.

This contribution would be achieved through delivering the following objectives for each of the site’s qualifying features:

  1. Avoid significant mortality, injury and disturbance of the qualifying features, so that the distribution of the species and ability to use the site are maintained in the long-term;
  2. b. Maintain the habitats and food resources of the qualifying features in favourable condition.

Further supplementary advice on the draft conservation objectives is provided in the Draft Conservation Objectives and Advice on Operations document.


Advice on operations

In line with Regulation (18) of the Offshore Marine Conservation (Natural Habitats, & c.) Regulations 2007 (as amended) and Regulation 33 of The Conservation (Natural Habitats &c.) Regulations 1994 (as amended in Scotland), the advice on operations identifies those operations (human activities) that may cause damage or deterioration to the qualifying species, or their supporting habitats, for which the Seas off St Kilda SPA has been classified. This information will be useful if you are developing, proposing or assessing an activity, plan or project that might affect the site.

The greatest direct threats to northern gannet, northern fulmar, common guillemot and Atlantic puffin from human activities are likely to be energy production and extraction of living resources (fishing) activities (based on best scientific evidence at the time of writing). However, all species might also be sensitive to pressures exerted by the following types of activity;

  • renewable energy developments: wind, wave and tidal;
  • marine hydrocarbon energy developments;
  • fishing activities;
  • disturbance from activities such as shipping and recreational boating/yachting;
  • military activities;
  • possibly industrial and agricultural liquid discharges and to waste disposal from munitions, but little is known, and this is not assessed due to lack of evidence.

These activities do not necessarily occur in or near the site at present, however they are important to bear in mind to avoid potentially damaging activities from occurring within the SPA in the future.

No assessments of sensitivity of European storm-petrel or any other petrel species to activities or pressures are available, and there is little evidence to help with assessments of what they might be sensitive to.

Any activity that can cause a pressure or pressures to which the feature may be sensitive could present a risk to the feature and affect whether conservation objectives are met; we advise competent authorities to manage these in order to reduce or remove the overall risk to the site’s qualifying features. Further advice on activities that can present a risk to the achievement of the site’s conservation objectives is available in the Advice to Support Management document.

Our scientific understanding of the ecology of the site, its integrity and its qualifying features, and how activities can affect them may change over time. JNCC’s conservation advice will be kept under review and will be periodically updated to reflect this.


Activities and Management

Last updated: December 2020

Management actions seek to avoid any adverse effects on the listed features from those pressures associated with human activities. All activities (on or off-site) should be managed to minimise disturbance and mortality of the bird features or the habitat and food resource on which they rely. The risk of impacting the local population level needs to be avoided to ensure the site’s conservation objectives are achieved.

JNCC and Scottish Natural Heritage (now NatureScot) has developed an Advice to Support Management document, to support discussions with stakeholders about the management of activities within this SPA. This paper considers a range of activities and developments taking place within the SPA, and focusses on where we consider there could be a risk of conservation objectives not being met.

This site forms part of the networks of MPAs across the UK and contributes to international networks such as that of the North-east Atlantic under OSPAR. As the UK is a contracting party to the OSPAR Commission, JNCC is committed to ensuring that the OSPAR MPA network is well-managed.

JNCC considers well-managed to mean the timely progress of an MPA around the 'MPA management cycle'. This involves:

  1. The documentation of appropriate management information – conservation objectives, advice on activities capable of affecting the protected features of a site, and spatial information on the presence and extent of the protected features of a site.
  2. The implementation of management measures – management actions considered necessary to achieve the conservation objectives of a site.
  3. Site condition monitoring programmes – collecting the information necessary to determine progress towards a site's conservation objectives.
  4. Assessment of progress towards conservation objectives – using available information to infer whether a site is moving towards or has achieved its conservation objectives.

Further information on the progress of the Seas off St Kilda SPA around each of the four stages in the MPA management cycle will be provided when available.



Last updated: September 2020

JNCC is currently leading on the development of options for biodiversity monitoring across all UK waters. JNCC’s advice for marine birds, which will include SPA monitoring, is anticipated to contain:

  • A summary of existing monitoring schemes which provide annual trends in abundance and breeding success of seabirds; and trends in the number of waterbirds using coastal sites to breed, stopover on migration or to over-winter; along with options to improve their precision;
  • Options for monitoring and surveillance of inshore and offshore aggregations of seabirds and waterbirds at sea and how these options can best be integrated with the above existing surveillance schemes (including whether co-ordinated monitoring of the existing/proposed marine SPA network can contribute to these);
  • Integration with indicator development work for Marine Strategy Framework Directive and OSPAR.

Information on monitoring of this SPA will be provided here when it becomes available.


Monitoring surveys

More detailed information on monitoring surveys at the site will be provided here when available.



Last updated: December 2020

Under Article 12 of the EU Wild Birds Directive (2009/147/EC), Member States are required to report every six years on their progress on the implementation of the Directive. Following the UK's exit from the European Union, this section will be updated to reflect the new assessment schemes once they are in place.


Published: .

This Site Information Centre (SIC) was created and last substantially updated prior to the end of the Transition Period following the UK’s exit from the European Union (31 December 2020). Therefore some of the content may still refer to EU legislation and management proposals or commitments which were correct at the time that the content was last updated. These references will be revised as necessary when the SIC is next substantially revised. Requirements through EU legislation are being retained in the UK so existing environmental protections and standards remain, and the protection given to habitats and species continues.

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