The productive waters of Newfoundland, Canada, render this region host to nationally and globally important breeding seabird populations. This study updates estimates and trends of three major populations using a Geographic Information System (GIS) approach to estimate occupied areas of high-density breeding seabirds, correcting for slope. Our results show that the Common Murre Uria aalge breeding population on Funk Island remains the largest in the western North Atlantic at 472 259 SE 32 740 (CI 398 669–545 849) pairs and increased at a rate of +0.3% per year between 1972 and 2009. The Atlantic Puffin Fratercula arctica colony on Great Island, Witless Bay, increased between 1979 and 1994 and continues to host the largest population of this species in North America at 174 491 (CI 147 559–201 423) breeding pairs estimated in 2011; the population has stabilized and may be showing signs of decline. Finally, Leach’s Storm-Petrel Oceanodroma leucorhoa breeding on Great Island, previously the second largest population in the western North Atlantic, has declined by 55% since 1979; it was estimated at 134 139 (CI 76,818–191,459) pairs in 2011, and is the lowest to date. Our GIS approach incorporated a 3D model to correct for slope of nesting areas; compared with traditional non-GIS techniques, this approach increased the estimated occupied area by 5%–10% for flat surfaces occupied by murres, by 16%–36% for moderate slopes occupied by storm-petrels, and by 40%–46% for steep slopes occupied by puffins. The application of newer tools such as high resolution satellite imagery and digital elevation models, coupled with GIS, are becoming more common and continue to improve the efficiency and accuracy of assessing occupied areas of highdensity breeding seabirds.
Keywords: geographic information system, monitoring, Newfoundland, population estimate, population trend, seabirds