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Comparison of growth rates and fledging weights recorded for Thick-billed Murre chicks (Uria lomvia) by previous investigators shows that these parameters vary widely between studies. We measured growth rates and fledging weights at four colonies in the Hudson Strait area to examine the magnitude of variation both within and among colonies. Significant variations among years and among different areas of a single colony were detected but found to be less important than colony-specific factors in determining overall variation. A negative correlation between colony size and chick fledging weights suggests that colony size may be an important determinant of intercolony differences.

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.

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