New research has shown that a large seabird colony on Ascension Island creates an "halo" where fewer fish can live.Ascension is a UK Overseas Territory that houses tens of thousands seabirds, of different species, whose prey includes flying fish.New research by the University of Exeter, Ascension Island Government and the University of Exeter found that flying fish numbers have dropped to 150km (more about 90 miles) from the island. This could only be explained with seabird foraging.These findings, which are rare evidence for a long-standing theory that was first presented at Ascension, show how food-limited seabird communities naturally are and why they are so sensitive to human fishing.Dr Sam Weber from the Centre for Ecology and Conservation at Exeter's Penryn Campus in Cornwall said, "This study tells a lot about large colonies of animals and their numbers are limited.""These birds are concentrated on Ascension Island during breeding season. The intensity of their foraging near the island is naturally the highest."As they consume the most readily available prey near the island, they must travel longer distances to eat, which causes the 'halo to grow outwards."Once people can't find enough food for their needs, they stop growing the colony.""Human impact such as fishing can disrupt this natural balance and have adverse effects on the populations of top predators marine like seabirds."What surprised me the most was the size of the footprint that we found.It shows that Marine Protected Areas might need to be large, as some predators depend on large prey stocks.After British ornithologist Philip Ashmole who proposed the idea after visiting Ascension Island 60 years ago, the pattern of prey loss revealed by the study is called "Ashmole’s halo".The researchers examined the regurgitated food of seabirds and tracked their foraging trips to determine if they were flying fish.Ascension's nesting seabird species include frigatebirds and masked boobies.###The Royal Netherlands Institute for Sea Research and the RSPB were part of the research team.The Study was funded by the Conflict, Security and Stability Fund of the UK Government and a Darwin Initiative grant.The paper was published in Proceedings of the National Academy of Sciences. It is entitled "Direct evidence of prey depletion and a 'halo' around a pelagic predator colony."
