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Two of the Animal Demography Unit's Honorary Research Associates, Rob Crawford and Jean-Paul Roux, are co-authors of an important paper published in the leading journal Science today. It provides critical guidance on how fish stocks should be managed in such a way that there is enough left over for the seabirds.
"Fishing can have devastating effects on seabirds. Not only do they get snagged on hooks and tangled in nets, but chronic overfishing can deprive the birds of their prey—the same small fish that boats are catching. Now a study has identified what appears to be a universal threshold for danger: when the biomass of so-called forage fish drops below one-third of its maximum, seabirds of many species start to have fewer chicks.
"'This is one of the most important seabird papers to be published in some time,' comments conservation biologist Dee Boersma of the University of Washington, Seattle, who was not involved in the research. The findings demonstrate the widespread reliance of seabirds on small forage fish, she says. To protect the birds, the papers' authors call for lower harvest levels of forage fish. 'The problem remains that most fisheries are not properly managed and controlled,' says co-author Philippe Cury of the Institute of Research for Development in Sète, France. Worldwide, about 25% of forage fish stocks have collapsed, he adds.
These are the first two paragraphs of the report that appears on the website of the journal Science. Read the full report here.
The abstract of the paper reads like this: "Determining the form of key predator-prey relationships is critical for understanding marine ecosystem dynamics. Using a comprehensive global database, we quantified the effect of fluctuations in food abundance on seabird breeding success. We identified a threshold in prey (fish and krill, termed “forage fish”) abundance below which seabirds experience consistently reduced and more variable productivity. This response was common to all seven ecosystems and 14 bird species examined within the Atlantic, Pacific, and Southern Oceans. The threshold approximated one-third of the maximum prey biomass observed in long-term studies. This provides an indicator of the minimal forage fish biomass needed to sustain seabird productivity over the long term." The full reference is Cury PM, Boyd IL, Bonhommeau S, Anker-Nilssen T, Crawford RJM, Furness RW, Mills JA, Murphy EJ, Österblom H, Paleczny M, Piatt JF, Roux J-P, Shannon L.J, Sydeman WJ 2011. Global seabird response to forage fish depletion – one-third for the birds. Science 334: 1703–1706.