Harbour seal (Phoca vitulina) COSEWIC assessment and status report: chapter 5
Habitat
Habitat requirements
P. v. concolor inhabits the near-shore, coastal waters on both Canada’s Arctic and Atlantic coasts and uses both aquatic and terrestrial habitats. They are well known for their use of estuaries and rivers, and have been recorded in excess of 200 km inland (e.g. Erlandson 1834; Strong 1930; Dunbar 1949; Wheeler 1953; Mansfield 1967; Beck et al. 1970; Paulbitski 1974; Roffe and Mate 1984; Williamson 1988; Bernhardt 2005). They haul out on both rocky and sandy substrates, often on isolated rocks and islets. Though Lesage et al. (1999) confirmed that the majority of dives performed by St. Lawrence estuary harbour seals were to depths of less than 4 m, data from other areas such as Sable Island demonstrate that harbour seals often dive to 80 m or more (Bowen et al. 2001a). On Sable Island, females spent more time diving and individual dives were deeper and longer as lactation progressed (Bowen et al. 2001a).
Because they lack elongated front claws, harbour seals cannot excavate holes in the ice like ringed seals (Pusa hispida). During Arctic winters, they are therefore reliant on permanent areas of open water that occur because of moving water or, where such areas do not exist, they must spend the winter at the edge of the fast ice (Mansfield 1967; Stewart and Lockhart 2005). Most seals monitored with satellite telemetry in the Churchill River wintered along the offshore sea ice edge near the river mouth (Bernhardt 2005). Animals also ventured into the pack ice during the winter, but did not move into water deeper than 50 m. Animals generally returned to the Churchill area during ice break up, and remained in open water until ice in the Churchill River estuary broke and animals were able to return to the haul-out (Bernhardt 2005).
Studies of P. v. mellonae have found no permanent haulout sites on Lacs des Loups Marins and Lac Bourdel (Consortium Gilles Shooner & Associés et al. 1991). In winter, when the vast majority of the lakes and rivers are covered in ice, the seals may rely on several physical features for their sources of air: areas that remain ice-free because of strong currents, fissures in the ice, and air pockets created by the shoreline's complicated geometry or by the undulations in the bottom of the sheet ice on the lake's surface (Smith and Horonowitsch 1987; Consortium Gilles Shooner & Associés et al. 1991; Dean Consulting & Research Associates 1991). It is not known where pupping occurs. Several authors have postulated that pupping takes place in under-ice shelters since the lakes are still iced over at the time of pupping, and no births have been observed on the ice (Consortium Gilles Shooner & Associés et al. 1991).
Habitat trends
Archeological data from bone assemblages suggest that during periods of warmer weather and presumably less ice, harbour seal bones had a higher frequency of occurrence compared to those of ringed seals in excavations along the coast of northern Labrador and southeastern Baffin Island. The opposite was true when the weather was cooler and there was more ice (Woolett et al. 2000). With current evidence indicating a shrinkage of Arctic ice (e.g. Grumet et al. 2001), some authors have suggested that harbour seals might become more abundant in the Arctic due to an increase in open water (Stirling and Derocher 1993; Derocher et al. 2004). Preliminary data from Inuit harvests and fatty acid signatures in polar bears indicate that harbour seals may be increasing in the area of western Hudson Bay (Derocher et al. 2004; Bernhardt 2005).
Lucas and Stobo (2000) speculated that harbour seals could be shifting their distribution southward because of changing environmental conditions. However, no shift in distribution has been reported in Newfoundland (Sjare et al. 2005). Broad patterns of local distribution recently observed by Sjare et al. (2005) are also consistent with those observed during the 1970s in Labrador by Brice-Bennett (1977) and Boulva and McLaren (1979).
Habitat protection/ownership
All harbour seal habitat in Canada (aquatic and terrestrial) is under the control of the provincial, territorial, or federal governments.
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