Photo: Baltic seabird project
In a unique study, researchers show surprising thresholds for seabird survival
In a recent article published in Science, researchers show that successful seabird breeding depends on access to one third of the world's fish.
In the most comprehensive study ever undertaken an international group of scientists, including Baltic Nest Institute researcher Henrik Österblom, show that many seabird species decline strongly when the food available for them in the ocean declines below a third of the maximum amount recorded.Seabirds are some of the best and most easily measured indicators when it comes to diagnosing the health of the world's marine ecosystems.
The study, which was recently published in Science, covers birds from the Arctic to the Antarctic and from the Pacific to the Atlantic. Österblom and his colleagues used data collected from 14 species including guillemots, gannets, puffins and penguins.
Global pattern
What they found was a remarkable global consistency between access to fish and seabird breeding success.
Wherever they occurred in the world the effect of low fish was similar. Österblom and his colleagues found that breeding reaches a plateau and does not change even as food abundance increases. When the amount of fish in the sea was greater than one-third of maximum levels of fish, the number of chicks produced remained pretty much unaffected. But if the fish abundance fell below this one-threshold, the number of chicks produced declined.
"The global pattern shows a threshold below which the numerical breeding response declines strongly as food abundance decreases," says Henrik Österblom.
Sufficient birds means healthy ecosystems
The study is not only interesting for its findings about the relations between seabirds and access to fish. It can also provide an overall indication of what state the world´s marine ecosystems are in.
"Determining the relationships between predator and prey is critical for our understanding of marine ecosystem dynamics," says Henrik Österblom.
He argues that the thresholds defined in the study can be implemented in management objectives to maintain forage fish biomass above the necessary one-third. Though there might be some variations between different fish populations, most of the economically important ones have sufficient data to define thresholds.
"Our study demonstrates a sufficient consistency to argue the one-third-for-the-bird principle could be applied widely," Österblom concludes.
