Low Seabird Densities in the Pelagic Environment of the Strait of Georgia, British Columbia

Seabird surveys in the pelagic environment of the Strait of Georgia, British Columbia, indicated an exceptionally low annual average density of 3.16 seabirds per km2 when compared to similar estimates of seabird densities in other south coastal British Columbia waters. In spite of a wide (20-km) pelagic zone the avifauna lacked most of the open ocean species and in fact was typical of the inshore protected waters of British Columbia. Two possible explanations were considered. First, though the biological productivity of the study area is not low the apparent absence of suitable foods, particularly adult Pacific herring, Clupea harengus pallasii (Valenciennes), may explain the low seabird numbers. Second, the discharge of the Fraser River which creates a highly turbid layer of surface water may seriously limit the effectiveness of visual predators