Nature reserve
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The island's cliffs are part of the South Stack Cliffs RSPB reserve which are home to an estimated 8,000 nesting birds during the breeding season. An RSPB visitor centre (with bird hide) is located at Elin's Tower on the mainland. Birds and marine life seen from the centre include choughs, peregrine falcons, and kestrels as well as harbour porpoises, grey seals, Risso's dolphins and bottlenose dolphins.
Tidal energy project[edit]
In 2019, proposals to develop a 35 km2 (14 mi2) 'West Anglesey Demonstration Zone' tidal energy project at South Stack were submitted under the Transport and Works Act 1992 to the Welsh Government for planning consent. Consent for the project, called Morlais was awarded in December 2021 and construction of the onshore grid connection works took place in 2023.
As the development will come within 500 metres (1,600 ft) of the South Stack SSSI, concerns have been expressed about the visual impact on the Anglesey Area of Outstanding Natural Beauty and the Holyhead Mountain Heritage Coast, along with the resultant impact on the tourism, recreation and fishing sectors. The developers have identified that seabird and mammal populations would be affected within the Holy Island Coast Special Area of Conservation and Special Protection Area along with the North Anglesey Marine Special Area of Conservation. Most notably bottlenose dolphin and harbour porpoise would likely be affected, whilst razorbill and common guillemot will be severely impacted. The RSPB is concerned that the razorbill colony on South Stack could be wiped out.