The Berwickshire and Northumberland coast is one of the most important areas in Europe for grey seal (Halichoerus grypus), with over 1,500 pups born in the area every autumn. There are two major grey seal breeding groups within the site.
There is a long established breeding population on the Farne Islands and a relatively recently established breeding group on the mainland coast at Fast Castle. In addition, to the north of the SAC, there is a major breeding colony on the Isle of May which is traditionally thought to have been established by recruitment from the Farnes population. There are smaller breeding groups to the west of the SAC on the small isles of the Firth of Forth, particularly Inchkeith. To the south of the SAC, the nearest significant breeding colony is at Donna Nook in Lincolnshire. Pups are occasionally born on other sections of the coast, and parts of the coast between Budle Bay and the north end of Holy Island would appear to be potentially suitable breeding sites; however, no other regular breeding groups are known within the SAC at present, other than at the Farne Islands and Fast Castle.
Farne Islands Breeding Colony
Grey seals have bred on the Farne Islands since historical records began in the 7th Century. Today (2013), an estimated 4,000 individuals live and breed on the Farne Islands, with approximately 1,000 pups being produced each year, although mortality can be high due to frequent bad weather and rough sea conditions. Females give birth on the Farnes from September through to December, often selecting sites close to where they gave birth in the previous season. On the Farne Islands, rocky and coarse sediment shores provide the main breeding habitats. Access to undisturbed pupping areas is a key requirement and the success of the Farne Islands colony is thought to be largely due to the undisturbed nature of the islands.
Fast Castle Head Breeding Colony
Small numbers of grey seal have been known to breed on beaches at the base of cliffs at Fast Castle since the late 1980s. The first comprehensive pup production surveys were carried out in 1997 when pup production was around 230. Pup production at Fast Castle continues to grow exponentially at an average rate of approximately 16.6% per annum (p.a.). It is generally assumed that a closed population of grey seals can grow at around 12% p.a. in the absence of density dependent effects, with the highest plausible fecundity and adult and pup survival levels. Sustained growth of 16.6% p.a. can only be achieved with additional recruitment from other breeding colonies. In the case of Fast Castle, it seems likely that the nearby Isle of May population is the main source of recruits. The most notable feature of the Fast Castle colony is that it has exhibited very rapid growth throughout a period when the adjacent colonies at the Farne Islands and the Isle of May have shown little growth. In 2008, Fast Castle pup production was equal to that of the Farne Islands. With no indication of a slow-down in the 16% p.a. growth rate, the obvious implication is that within a few years this remote colony on the Berwickshire coast will be significantly larger than the Farne Islands colony.