Throughout history, humans have managed to spread across the globe, inhabiting some of the most inhospitable environments. We have come and we have gone from areas for a number of reasons, but we have always managed to settle somewhere. Usually (not always) our movements are not reflective of our environments and we would not class ourselves as ‘bio-indicators.’ However, though the movements of humans may be very uninteresting and not much to worry about, the movement or lack of other species can be a cause for concern. On the remote Scottish island of St Kilda, the lack of a number of species is proving serious concern. Who are we missing? Our seabirds.
St Kilda is the known to be the largest seabird colony in the northeast Atlantic and has been designated by the United Nations as a World Heritage site for natural wonders. St Kilda hosts a number of species including kittiwakes, puffins, Manx-shearwaters, gannets, guillemots and Leach’s storm-petrels. However, over the last 16 years, the populations of seabirds on St Kilda have suffered monumental crashes, with ten of thousands of birds starving to death. What is the problem? Climate change. Rising ocean temperatures is one of the greatest concerns attached to climate change and rising water temperatures in the Atlantic has caused major shifts in the marine ecosystem. Seabirds are a major part of this ecosystem and the warming waters are putting a huge strain on their feeding behaviour. Between the years of 1999 and 2015, the populations of guillemots, fulmars and razorbills has dropped by 50-70%. Kittiwakes have also suffered huge declines of 90% and are thought to be heading for extinction. The National Trust for Scotland, which coordinates the monitoring of these seabirds, has stated that this seasons there was only one kittiwake nest over a total of 7 monitoring sites. Although the nest did produce a chick, it later died.
The island of St Kilda is a globally important site for these seabirds, with 17 different species being found here and up to 1 million individual birds staying here over the breeding season. In 2015 there were 276 kittiwake nests, a fall of 89% since 1999! Guillemot numbers have fallen from 17,438 to 8,206, razorbills have experienced a drop of 69% with numbers this year being only 718 and fulmar numbers have dropped from 62,000 to 27,000. The rising ocean temperatures have been the main problem for the seabirds, affecting their main food source of sand eels.
Seabird populations are a vital part of the marine ecosystem and their falling numbers are indicative of major shifts in marine ecology. The marine food web is a complex one, but we know that approximately 95% of the diet of many seabirds is made up of sandeels. Sandeels are central in the marine food web and they are highly sensitive to the changes in the ocean environment. Sandeels experience pressures from below as physical conditions and plankton communities change, but also pressures from above, such as predation and over-fishing. As ocean temperatures rise, particularly the sea surface temperature, plankton, a major food source of sand eels, go in search for cooler waters, moving deeper into the ocean, or further north to colder waters. Over the past 30 years, plankton communities are thought to have migrated north by 1000 kilometres and the sand eels are moving with them. This has a huge impact on seabirds as it makes their main food source more difficult to locate and creates more failed fishing attempts. Although there are other factors likely to be at play, including over-fishing from humans, plastic pollution and predation, climate change is the biggest threat to the ecosystem.
The decline in seabirds is sending a worrying message concerning the state of the marine environment. RSPB Scotland has expressed its concern over recent findings and stated that even though the Scottish Governments pledge to cut carbon emissions was a positive step, more needs to be done to protect these valuable species. Seabird island restoration projects and the development and management of the network of Scotland’s marine protection areas are where the future of our birds may lie and RSPB Scotland has stated that it is critical that such initiatives work.
Changes in the marine environment are always difficult to monitor as they cannot be well observed. The changes in our species populations are the best indicators we have of the state of the marine ecosystem and highlight the effect that climate change is having on our wildlife. The National Trust for Scotland is now launching a fundraising appeal called ‘Love Our Islands’, aimed at protecting Islands such as St Kilda and their coastal areas.
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