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Location United Kingdom, Wales
Central coordinates 5o 28.79' West  51o 43.85' North
IBA criteria A4ii, A4iii, B1ii, B2, C3, C4
Area 11 ha
Altitude 0 - 15m
Year of IBA assessment 2007

Royal Society for the Protection of Birds

Site description A low-lying, flat-topped basalt island situated about 18 km west of the mainland Dyfed coast. Vegetation is limited by exposure to wind, salt spray and the large numbers of seabirds. The site is important for its seabird colonies, including a very large gannetry.

Populations of IBA trigger species

Species Season Period Population estimate Quality of estimate IBA Criteria IUCN Category
Northern Gannet Morus bassanus breeding  2004  32,094 breeding pairs  poor  A4ii, B1ii, B2, C3  Least Concern 
A4iii Species group - seabirds breeding  1999-2001  31,611 breeding pairs  poor  A4iii, C4   

IBA Monitoring

2007 high favourable high
Good - based on reliable and complete / representative data

Biological resource use fishing & harvesting aquatic resources - unintentional effects: large scale happening now whole area/population (>90%) slow but significant deterioration high
Climate change and severe weather habitat shifting and alteration likely in long term (beyond 4 years) majority/most of area/population (50-90%) moderate to rapid deterioration medium

Morus bassanus Northern Gannet 33000 32094 breeding pairs 98 favourable
Species group - seabirds A4iii 33510 31611 breeding pairs 95 favourable

Whole area of site (>90%) covered by appropriate conservation designation  A comprehensive and appropriate management plan exists that aims to maintain or improve the populations of qualifying bird species  Substantive conservation measures are being implemented but these are not comprehensive and are limited by resources and capacity  high 

Protected areas

Protected area Designation Area (ha) Relationship with IBA Overlap with IBA (ha)  
Grassholm National Nature Reserve 11 is identical to site 11  
Grassholm RSPB Reserve 11 is identical to site 11  
Grassholm/ynys Gwales Site of Special Scientific Interest 11 is identical to site 9  
Pembrokeshire Coast National Park 58,400 protected area contains site 11  


IUCN habitat Habitat detail Extent (% of site)
Grassland   -
Coastline Rock stacks and islets; Sea cliffs and rocky shores  -

Land use

Land-use Extent (% of site)
nature conservation and research -
tourism/recreation -

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Recommended citation  BirdLife International (2016) Important Bird and Biodiversity Area factsheet: Grassholm. Downloaded from on 28/10/2016

To provide new information to update this factsheet or to correct any errors, please email BirdLife