Distribution of seabirds in the Lower Estuary and Gulf of St Lawrence (Canada) during summer
1 Research and Technology Centre (FTZ), University of Kiel, D-25761 Büsum, Germany;
2 Canadian Wildlife Service, Environment Canada, 801-1550 Avenue d'Estimauville, Québec G1J 0C3, Canada.
We investigated the abundance and distribution patterns of a range of seabird species in the Lower Estuary and Gulf of St Lawrence in the western North Atlantic Ocean using ship-based surveys during the summers of 2007, 2008 and 2009. This area is known to be of particular importance for several seabird and cetacean species. We analysed distribution and abundance of common seabird species in mid and late summer, and estimated total numbers for the Southern Gulf, which was most intensively surveyed. Northern Gannets Morus bassanus were overall most abundant and widespread. Our at-sea estimate of 150,000 birds for the Southern Gulf constitutes 64% of the North American breeding population, rendering the site one of the most important areas for this species worldwide during this period. Our at-sea estimates suggest that according to the 1% threshold of the Ramsar Convention considerable proportions of the Canadian breeding population of Razorbills Alca torda (5-11%), Common Guillemots Uria aalge (2-3%), Black-legged Kittiwakes Rissa tridactyla (2-4%) and Black Guillemots Cepphus grylle (1-2%) use the Southern Gulf. Relative to their biogeographic populations, at-sea totals were also considerable in American Herring Gulls Larus smithsonianus (3-4%), Great Black-backed Gulls L. marinus (1-4%) and Great Northern Divers Gavia immer (1-4%). Areas of high seabird densities and multispecies aggregations (hotspots) occurred around the Gaspé Peninsula (Northern Gannets, alcids, Black-legged Kittiwakes, Larus gulls), in the Northwestern Gulf, along the Lower North Shore (near St Mary's Islands), along the west coast of Newfoundland (Bay of Islands to St Georges Bay), in Cabot Strait, around Cape Breton Island and the Magdalen Islands, as well as west and east of Prince Edward Island.
Since the 1960s, considerable effort has been directed at surveying seabirds in the marine environment. Previous studies resulted in detailed publications on seabird distribution and estimated total numbers of seabirds at sea (e.g. Brown et al. 1975; Brown 1986; Skov et al. 1995; Sonntag et al. 2006; Garthe et al. 2007a). The methods for ship-based surveys started with qualitative approaches, collecting data on the relative abundance of seabirds as for PIROP (Programme Integré de Recherches sur les Oiseaux Pélagiques) in Canada (Brown 1986). Standardisation and improvement of survey methods (Tasker et al. 1984) has led to widely used and compatible protocols (e.g. Garthe et al. 2002; Camphuysen et al. 2004; Gjerdrum et al. 2012). Many current survey programmes apply distance sampling (Buckland et al. 2001) for clearly defined sampling units (e.g. adjusted line-transect) to account for imperfect detection of animals. These approaches enable the estimation of total numbers at sea for large marine areas (e.g. Sonntag et al.
2006; Garthe et al. 2007a; Fifield et al. 2009). We applied these methods to gain information on the current distribution patterns of the most common seabirds in the Lower Estuary and Gulf of St Lawrence.
The study area is a highly productive marine area (White & Johns 1997; Dufour & Ouellet 2007) holding important breeding colonies of Northern Gannets Morus bassanus, alcids, and Black-legged Kittiwakes Rissa tridactyla (Cotter & Rail 2007; Rail & Cotter 2007; Cotter et al. 2012; Chardine et al. 2013). The area has been subject to profound changes, such as the collapse of demersal fish stocks, which have altered the structure of the marine ecosystem, with fundamental effects on many fish species (e.g. Savenkoff et al. 2007a,b; Bundy et al. 2009) that are important prey for a multitude of seabirds. Moreover, seabirds were intensively surveyed at sea in this area during the 1970s and 1980s (Brown 1986), but only little effort was subsequently available between the 1980s and 2006 and current and easily available information is lacking. We identified areas of high seabird densities and multispecies aggregations (i.e. hotspots) in the entire Gulf and Lower Estuary and estimated total numbers at sea for common seabird species in the Southern Gulf to characterise its importance in a regional and international context.
We are sincerely grateful to Alain Gagné from the Maurice Lamontagne Institute (IML) in Mont-Joli, Tom Hurlbut from the Gulf Fisheries Centre in Moncton, François Grégoire (IML), Charline Lévesque (IML) and their colleagues for the opportunity to join their research cruises and for their kind support throughout these ventures. We thank the crews of the 'Teleost' and other vessels we worked on for their support and cooperation during the surveys. We also thank Jean-François Rail and Carina Gjerdrum from the Canadian Wildlife Service in Québec City and Dartmouth very much for providing data on seabird colonies and population estimates. Andy Webb, Iain Stenhouse and Martin Heubeck made valuable comments on earlier drafts of our manuscript, which greatly improved the quality of our paper.
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