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Scottish Natural Heritage BIODIVERSITY INDICATOR S005 – Dec 2016 The numbers and breeding success of seabirds Scotland’s twenty four species of breeding seabirds are of international importance. Seabirds are useful and important indicators for assessing the state of the marine environment. They rely on the sea, but breed on land making them relatively easy to monitor. They respond to a range of factors such as changes in food availability, weather, predation and pollution. Being relatively long lived the numbers of breeding seabirds usually changes slowly over time. Breeding success (the number of chicks produced) provides an indication of food availability (generally fish and other marine species) and other factors such as predation during the breeding season. Breeding success typically varies far more from year to year than breeding numbers. Northern gannet © Lorne Gill, SNH Evidence The indicators of breeding numbers for 12 species, and breeding success for 12 species, out of the 24 seabird species that breed in Scotland, are based on estimates from a representative sample of seabird colonies around Scotland. These are monitored as part of the UK Seabird Monitoring Programme, which started in 1986. The numbers and breeding success of seabirds in Scotland, 1986-2015 Breeding numbers 120 100 60 2015 2014 2013 2012 2011 2010 2009 2008 2007 2006 2005 2004 2003 2002 2001 2000 1999 1998 1997 1996 1995 1994 1993 1992 1991 1990 1989 1988 1987 1986 40 Breeding success 120 100 80 60 NOTE: The axes are not scaled to zero Year Assessment From the start of the time series in 1986 to the most recent estimate in 2015: • The mean numbers of 12 species of breeding seabirds in Scotland declined. By 2015, breeding numbers was 50% of the 1986 level. • Mean breeding success of 12 breeding seabird species has declined. TREND Decreased DATA CONFIDENCE http://www.snh.gov.uk/indicators/ Medium 2015 2014 2013 2012 2011 2010 2009 2008 2007 2006 2005 2004 2003 2002 2001 2000 1999 1998 1997 1996 1995 1994 1993 1992 1991 1990 1989 1988 1987 40 1986 Index 1986 = 100% 80 Commentary Included in this indicator are 16 i of the 24 species of seabird that regularly breed in Scotland. All seabird species included in this indicator are either Red or Amber listed as Birds of Conservation Concern (Eaton et al., 2015). Five are Red listed (European shag; Arctic skua; Atlantic puffin; black-legged kittiwake; and herring gull) and the remaining eleven are Amber listed. Out of the 12 species assessed for breeding numbers, Arctic skua has declined the most (-76%). The Northern Isles are their breeding stronghold and there have been declines in the availability of sandeels, which they obtain from other seabirds, such as kittiwake, by chasing to make them release their food. Increased predation from great skua has also been linked to their decline (Meek et al., 2011). No species show an overall increase in the indicator, though the numbers of common guillemot, common tern, Arctic tern and Sandwich tern have shown a slight increase from 2011 to 2015. Breeding success varied amongst the 12 species assessed. In 2015, it was higher than the long-term (1986 to 2014) average for six species: Arctic skua; black-legged kittiwake; common tern; common guillemot; northern gannet; and Sandwich tern. Three species had breeding success lower than the long-term average: herring gull; little tern; and northern fulmar. Three species had breeding success in 2015 around the long-term average: Arctic tern; Atlantic puffin; and great skua. A recent survey of northern gannet (Murray et al., 2015), has shown a large increase in their breeding numbers. Good breeding success and improved survival of immature and adult birds has helped boost populations and led to an expansion of their range. Source data and updates The indicator has been updated with data up to and including 2015. Breeding numbers trends are based on 12 species and the breeding success trend on the 12 species for which sufficient data are available ii. Data are derived from the UK Seabird Monitoring Programme (SMP) and its partners. The SMP collects and collates data on breeding numbers, demographic parameters (including breeding success and survival rate), and diet from a sample of colonies around the UK. The data confidence has been reduced to medium as it is over fifteen years since the last national census. The census provides an accurate snapshot of seabird breeding numbers and allows us to benchmark the annual colony counts. Updates are provided annually and the data are available from JNCC. UK Indicators JNCC reports on seabird population trends as an Official Statistic (see http://jncc.defra.gov.uk/page-4235). As Scotland supports the majority of UK breeding seabirds, the UK trend is greatly influenced by trends in Scotland. Seabird abundance in the UK increased between 1970 and 1999, and has since declined. References Eaton, M., Aebischer, N., Brown, A. et al. 2015. Birds of Conservation Concern 4: the population status of birds in the UK, Channel Islands and Isle of Man. British Birds, 108, 708-746. Meek, E.R., Bolton, M., Fox, D. and Remp, J. 2011. Breeding skuas in Orkney: a 2010 census indicates densitydependent population change driven by both food supply and predation. Seabird, 24, 1-10. Murray, S., Harris, M.P. and Wanless, S. 2015. The status of the gannet in Scotland in 2013-14. Scottish Birds, 35, 3-18. i Data available for 1 = Breeding Numbers 2= Breeding Success Arctic skua1,2; Arctic tern1,2; Atlantic puffin2;black guillemot1;black-legged kittiwake1,2;common gull1;common tern1,2;European shag1; great black-backed gull1; great skua2; common guillemot1,2; herring gull1,2;little tern1; northern fulmar1,2; northern gannet2; Sandwich tern1,2 ii Note: No data were available for lesser black-backed gull in 2015 and this has been removed from the indicator http://www.snh.gov.uk/indicators/