Global seabird response to forage fish depletion – one-third for the birds

Determining the form of key predator-prey relationships is critical for understanding marine ecosystem dynamics. Using a comprehensive global database, we quantify the effect of fluctuations in food abundance on seabird breeding success. We identify a threshold in prey (fish and krill, termed forage fish) abundance below which seabirds experience consistently reduced and more variable productivity. This response is common to all seven ecosystems and fourteen 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.