Grey and harbour seals in France: Distribution at sea, connectivity and trends in abundance at haulout sites

Abstract

Grey (Halichoerus grypus) and harbour seals (Phoca vitulina) are sympatric seal species, but they display distinct strategies of habitat use and connectivity between haulout sites. The distribution patterns and variations in relative abundance of both species were investigated along the French coast of the English Channel, at the southern limit of their range where seal numbers are increasing. Regular censuses conducted at all main haulout sites in mainland France showed significant seasonal variations at most sites, with more harbour seals counted during summer (breeding and moulting seasons), and more grey seals during summer only in the eastern English Channel. Trends in maximum haulout numbers at haulout sites showed a significant increase over the last five years, ranging from 9.7 to 30.9% per year for harbour seals, and from 5.8% (in the western English Channel) to 49.2% (in the eastern English Channel) per year for grey seals. These rates of increase in grey seal numbers are not linked to local pup production and most probably result from seal movements from the southwest British Isles and the North Sea, respectively. Aerial surveys conducted across the English Channel showed that most seal observations at sea were concentrated in the northeastern English Channel. Telemetry showed that the 28 harbour seals tracked remained highly coastal, within a radius of 100km from their haulout sites, and did not move to other known colonies. Grey seals moved much greater distances, reaching up to 1200 km from their capture site. More than half of the 45 grey seals tracked crossed the English Channel, especially during the breeding season, moving to known colonies in the southwest British Isles and the North Sea. Combining individual tracks and long-term surveys of the seal populations allowed a better understanding of the dynamics of these populations and their connectivity at a larger regional scale. The findings provide direct information for the management of grey and harbour seals within the frame of the Marine Strategy Framework Directive, and highlight focus areas where potential interactions between the two species should be monitored.

Habitat and resource segregation of two sympatric seals in the North Sea

“…2F) allows a good distinction of grey seals and harbour seals living along the German coasts. The coastal distribution of harbour seals in the southeastern North Sea compared to grey seals may explain the higher Hg concentrations we found (Table 1) (Tougaard et al 2008;Cunningham et al 2009;Herr et al 2009;Dietz et al 2012;Sharples et al 2012;Aarts et al 2016;Vincent et al 2017;Jensen et al 2018;Aarts et al 2019). In general, mercury contamination appears to reflect the known inputs into coastal waters suggesting the addition of mercury of industrial origin at coastal sites (Sergeant and Armstrong 1973).…”

“…If the number of seals increased along the German coasts during the foraging season, this may lead to wider foraging distributions of grey seals to find their preferred prey in response to the intra-and inter-specific sharing of food resources and in order to avoid competition for food resources. Many studies show the philopatric aspect and the coastal distribution of harbour seals in the Wadden Sea and around the North Sea basin (Tougaard et al 2008;Cunningham et al 2009;Herr et al 2009;Dietz et al 2012;Sharples et al 2012;Aarts et al 2016;Vincent et al 2017;Jensen et al 2018;Aarts et al 2019) contrasting with long trip durations and mostly offshore movements of grey seals (Bowen and Harrison 1994;Hall et al 1998;McConnell et al 1999;Herr et al 2009;McClintock et al 2012;Huon et al 2015;Aarts et al 2016;Vincent et al 2017;Scharff-Olsen et al 2018). Moreover, grey seals sampled along German coasts shown lower δ 15 N values and higher δ 34 S values and Se concentrations than harbour seals (Table 1).…”

“…Grey seals and harbour seals in the North Sea use the same areas on land and at sea, are mainly piscivorous, and have comparable life cycles (McConnell et al 1999;Brown et al 2012). Nevertheless, the annual breeding and moulting cycles of grey seals and harbour seals in the North Sea are asynchronous (Hall and Thompson 2009;Burns 2009) but their at-sea distributions during foraging trips may overlap and foraging occurs at the same time for a large part of the year (McConnell et al 1999;Herr et al 2009;Sharples et al 2012;Vincent et al 2017). They may therefore be expected to display spatial and/or resource partitioning to some extent.…”

Competition between marine mammals and fisheries in contemporary harvested marine ecosystems

“…To determine marine mammal-fisheries spatial and temporal overlap, firstly, information on marine mammal distribution and abundance is primarily acquired through systematic land-or boatbased observations (see Godwin et al 2016, Vincent et al 2017, large scale and aerial surveys of vast marine areas frequented by cetaceans as well as seal and sea otter haul out sites (e.g. Huber et al 2001, Laidre et al 2001, Bodkin et al 2002, Lonergan et al 2007, Bauer et al 2015, 2017.…”

Large‐scale molecular diet analysis in a generalist marine mammal reveals male preference for prey of conservation concern

“…Worldwide, harbor seals tend to move little, from dozens to 100 km from their haul-out site (Blanchet, Lydersen, Ims, Lowther, & Kovacs, 2014;Suryan & Harvey, 1998;Thompson & Miller, 1990;Vincent et al, 2017), sometimes covering even longer distances (Björge, Oien, Hartvedt, Bothun, & Bekkby, 2002;Lesage, Hammill, & Kovacs, 2004;Lowry, Frost, Ver Hoef, & DeLong, 2001;Sharples, Moss, Patterson, & Hammond, 2012). Males appear to move farther and have larger core areas than females, at least in certain regions (Blanchet et al, 2014;Thompson et al, 1998).…”