Seabird numbers and prey consumption in the North Atlantic

Abstract

We compared seasonal composition, abundance, and biomass of seabirds between the Northeast (ICES region) and Northwest (NAFO region) Atlantic fisheries regions to identify differences in community assemblage and prey consumption. Seabirds were more abundant in the Northwest Atlantic, but biomass was greater in the Northeast. This disparity resulted from enormous numbers of little auks Alle alle breeding in West Greenland and of Leach's storm-petrels Oceanodroma leucorhoa breeding in Newfoundland, plus large numbers of non-breeding shearwaters Puffinus spp. entering southern NAFO areas in summer. The Northeast Atlantic communities were dominated numerically by northern fulmars Fulmarus glacialis, large auks Uria spp., and the Atlantic puffin Fratercula arctica. Seabirds occupying the North Atlantic consume approximately 11 Â 10 6 t of food annually. Overall consumption rates peak during summer as a result of increased breeding activity and seasonal movements of birds into the North Atlantic. Because of the greater biomass of birds in the northeast, consumption (mainly by piscivores) in ICES areas was approximately 20% higher than that in NAFO areas, where planktivores dominate. NAFO areas had, however, a much greater consumption rate per unit area than ICES areas. Comparative studies such as these could prove informative in assessing large predator responses to the influence of fishing and ocean-scale climate change.

Trans-equatorial migration and habitat use by sooty shearwaters Puffinus griseus from the South Atlantic during the nonbreeding season

“…This study is the first to reveal details of the spectacular migration that annually sees millions of southern hemisphere Puffinus shearwaters flood the productive waters of the northwest Atlantic, to become the primary avian consumers of fish during the northern summer (Barrett et al 2006). While it has long been known that both adults and immatures of the more numerous great shearwater migrate to the North Atlantic (Brown 1988), we confirm this also to be the case for adult sooty shearwaters breeding in the Atlantic (cf.…”

“…In the Atlantic, sooty shearwaters are highly migratory, switching hemispheres between breeding and nonbreeding seasons to exploit productive foraging sites in the South and North Atlantic, respectively; sites that are used by a diversity of top predators year-round (Croxall & Wood 2002, Barrett et al 2006, Phillips et al 2006, Guilford et al 2009. After departing the breeding grounds, the shearwaters commence a rapid northward migration that is followed by an extended period of residence (143 ± 10 d) in the North Atlantic.…”

“…Sooty shearwaters therefore integrate resources annually over whole ocean scales, and this has led to the suggestion that their populations may serve as important indicators of both climate change and ocean 'health' (Shaffer et al 2006). In the northwest Atlantic, migrant great Puffinus gravis and sooty shearwaters from the southern hemisphere are the major avian consumers of fish during the northern summer (Barrett et al 2006); however, there is very little information on the provenance or the age classes of the latter. Spring and summer shipboard observations of sooty shearwaters in fresh plumage off eastern Canada (Scotian Shelf, Newfoundland Grand Bank and Labrador Sea), led Brown (1988) to conclude that the portion of the population migrating to the North Atlantic likely consisted of immature birds.…”

Small birds, big effects: the little auk (Alle alle) transforms high Arctic ecosystems

“…This area is the main breeding ground of the little auk (Alle alle), a small (approx. 160 g), zooplanktivorous alcid, which is the most abundant seabird in the North Atlantic [22,23]. Within a range of approx.…”

The feeding ecology of little auks raises questions about winter zooplankton stocks in North Atlantic surface waters

“…This population is composed, to a large extent, of birds breeding in northwest Greenland, east Greenland and Svalbard (Stempniewicz 2001). The number of little auks wintering off southwest Greenland is therefore estimated as 20 -40 million birds (Karnovsky & Hunt 2002;Barrett et al 2006). During winter (December -January), the mean depth of dives was 12 + 11 m, with a maximum dive depth of 50 m (n ¼ 6056 dives).…”