Between 2000 and 2008, the total number of seabirds breeding in the UK is believed to have decreased by approximately 9%. Breeding success has also declined over the same period. Climate change is partly responsible.
Trends vary between regions. Populations in the Irish Sea region increased on average by 37% during 1986-2007, in contrast to populations in the Eastern English Channel region, the Minches and Western Scotland region and over the Scottish Continental Shelf, which declined on average by 35-48% over the same period.
Mean breeding success has declined since 2000. As with population size, regional differences were apparent. Extremely low values were recorded for the Minches and Western Scotland in 1993, 1998 and 2005-7, but were generally higher than the other Regional Seas. Breeding success for the Scottish Continental Shelf region was lower than average, with mean success in this region very low in 1998, 2001, 2003-5 and 2007.
Evidence suggests climate change, in particular warmer winters, has resulted in major changes in the plankton in the North Sea that have probably reduced the availability and nutritional quality of seabird prey such as sandeels. Data on breeding success of species most sensitive to food shortages such as Arctic skua, kittiwake and shag suggest that climate impacts are greatest in the northern North Sea and Scottish Continental Shelf.
Continued poor breeding success and reduced survival will lead to further declines in some seabird populations in the short and long term.
Models predicting the future range of seabirds under climate change suggest that, by the end of this century, great skua and Arctic skua will no longer breed in the UK and the range of black guillemot, common gull and Arctic tern will shrink so that only Shetland and the most northerly tips of mainland Scotland will hold breeding colonies.
Climate-linked reductions in food supply can have a dramatic impact on the social fabric of colonies, with cases of infanticide recorded in guillemots for the first time.
Increased storminess may reduce available breeding habitat for shoreline-nesting species (e.g. terns), wash away nests and create unfavourable foraging conditions leading to starvation.