Kittiwake numbers have been declining from a number of years, the sound that was once familiar at Sumburgh, Noss and Hermaness are becoming quieter. In Shetland since 2000 Kittiwakes have declined by 87% and this is down to the lack of sand eels.
The combination of over fishing an Global warming has seen the sea temperatures increase the sand eels dive deeper making it difficult for surface feeding Kittiwakes to find food. Even Puffins and guillemots are finding it difficult.The RSPB indicate that it wont be long until the Kittiwakes completely disappear as a breeding bird from the cliffs of Shetland.
Oceanic climate change is forcing the marine animals to either change their habits or move away to another area. A recent study for example has indicated that a 2-3% increase in sea temperatures may lead to a 20-30% decrease in marina species. All marina mammals have a limited temperature range in which to live in. With sand eels the whole process of breeding, feeding, growth, defense and behavior is affect by the increase in the ocean temperature.
The number of new species entering our ocean is increasing as these warmer tolerant creature start to compete for food or become predators. You only have to look at the prey items that kittiwakes are finding to appreciate that their food source has moved deeper.
The pipe fish that many birds bring are long and have many bones, lacking in protein and difficult for young birds to swallow, with some chocking to death.
Sand eels seem to be moving deeper in the ocean as a result of these effects as a result many birds are now finding this prey item out of their reach.
Man has influenced the abundance of fish and other marine creatures and it has been estimated that 400 million people depend on fish as a food source. The sand eel fisheries around Shetland had been mainly concentrated around the south mainland, where seabird colonies suffered at Sumburgh, Noss and Noness.
Fishing together with combination of other factors has lead to a big decrease in sand eel numbers which have never recovered. Sand eels are only used for pet food and fertilizers It is widely understood that the population needs a third of their stock to survive in any given year to support seabird colonies.
The BTO has studied seabird populations for some time and they indicate that colonies on the west of Britain are fairing better than the east and north coast colonies. Studies indicate where sand eel fishing has taken place seabirds have been most affected.
Even though sand eels are no longer fished in Shetland, the species is largely sedentary making it difficult for populations to recover. Danish fishing vessels are the only one that still fish for sand eels, but predatory fish such as Cod, Haddock, Whiting and Saithe do have an impact no sand eel numbers and further research is being done
Some seabirds have already responded to the changes in temperature by moving further north. Changes also encourage birds to breed earlier and therefore may not be in time for food prey abundance. We will see over the coming years through various studies how these changes will further effect our seabirds, so for now we have to enjoy the sight and sounds of a seabird colony but scientist have predicted a 2 degree warming of our oceans by 2050.
This year I have noticed a good number of Arctic Terns bringing sand eels back to the nest throughout the season, but only a very few Puffins have been bring food back. The other day down at Sumburgh a few Guillemot young could be seen and some adults with fish.
Lerwick harbour was full of birds with gannets catching good numbers of fish and even Kittiwakes and terns seem to be doing OK. Both Arctic and Gt Skua could be seen chasing birds. Its far too early to say how good or bad the season has been but this is the busiest year for birds with fish for a considerable time.