Common risks among declining marine predators suggests ecosystem change

Identifying drivers of ecosystem change in large marine ecosystems is central for their effective management and conservation. This is a sizable challenge, particularly in ecosystems transcending international borders, where logistical constrains can hinder effective monitoring and conservation. In public health, epidemiology helps target goals of preventive medicine by identifying risk factors of health-related states or events, and thus better inform policy decisions. We use this approach in the Salish Sea—a 17,000-square-kilometer transboundary marine ecosystem in North America’s Pacific Northwest—to discern risks increasing the likelihood of species undergoing population declines within a community of marine birds, and thus pinpoint possible drivers of ecosystem change. Using survey data from long-term monitoring programs run by federal, state and provincial wildlife agencies as well as citizen science, we identified specific foraging strategies and natural histories linked with declines in Salish Sea winter counts among 39 taxa of marine birds. We found that species most at risk of experiencing declines were pursuit divers that specialize on forage fish species for prey, such as common murres (Uria aalge) and western grebes (Aechmophorus occidentalis). Life at sea is intrinsically perilous for most marine bird species, and while the synergy of a combination of risk factors is most likely driving declines of diving birds in the Salish Sea, changes in the availability of low-trophic prey may be increasing the challenges diving birds face. This synthesis of long-term ecological monitoring using an epidemiological framework can help elucidate potential drivers of local extinctions and ecosystem change in large marine ecosystems—information that is paramount for species-specific and ecosystem-wide conservation