Harbour seals, residents or seasonal visitors?

The harbour seal has a precarious status in the St. Lawrence. This small population, probably less than 2000 individuals in the Estuary, is one of the most contaminated of the marine mammals. It is important to understand how this population lives in its habitat to help direct conservation strategies.

To go through the looking glass

In one study carried between August 1997 and July 1998, seven harbour seals were fitted with satellite transmitters in the Rimouski area. The signals sent to the satellite allowed researchers to follow the movements of these animals and to discover the depths of their dives. Other seals had a time, depth, and speed recorder (TDR) attached to them. This gadget collects detailed information about the underwater behaviour of the animals without providing precise data on its actual position. These seals were also equipped with a probe which recorded the temperature of the stomach, the temperature dropping sharply every time the seal swallowed a fish.

In another study, seven harbour seals were equipped with satellite transmitters in the fall of the years 1994 to 1997 to follow their winter movements. Fifteen other harbour seals carried TDRs and radio transmitters between May and September of the years 1995 to 1997. Their positions were recorded on a regular basis by researchers at sea.

In short...

The study carried between August 1997 and July 1998 showed that the harbour seal does not undertake the long migrations of the other species of seals in the Atlantic. Three of the seals actually spent the winter in the exact same sector in which the tracking began in August. As well, the seals fitted with the TDR and the stomach probes were feeding at relative proximity to their haul-out sites and for half of the time stayed within 4 metres of the surface.

The other study challenges these conclusions. When ice formed in bays, four of the seven seals tracked by satellite—all of them adult males from the Métis area—left their summer haul-out site and migrated over respective distances of 520, 330, 150 and 65 km. Two of these animals migrated further upstream in the St. Lawrence Estuary (to Bic and Blanche Island respectively), and the two others towards the Gulf of St. Lawrence. As for the three other seals that were tracked using satellite technology—one female and two immature seals—they did not undertake a long winter migration. Instead, they remained near their respective summer haul-out sites of Métis, Bic and Blanche Island, respectively. Harbour seals are known to have a low tolerance for severe ice conditions. The movements detected using satellite transmitters clearly corresponds with migrations from haul-out sites where ice became thick in winter towards sites where ice conditions were less severe. Lastly, satellite and TDR tracking confirm that during periods of no ice harbour seals remain near the shore in areas where water depth does not exceed 50 m and undertake only short forays.

A greater number of tracking bouts is required to learn more about the seasonal migrations of harbour seals and to establish if gender and age are determining factors. The fact that some harbour seals are relatively sedentary residents of the St. Lawrence accentuates certain risks that have been identified in other studies, such as contamination through the food chain, disturbance on haul-out sites and habitat loss.

Project collaborators

Partners:

St. Lawrence Action Plan–Vision 2000, Parks Canada, Fonds pour les chercheurs et l’aide à la recherche du Québec (FCAR), Natural Science & Engineering Research Council of Canada (NSERC), Canadian Wildlife Foundation, University of Waterloo Graduate scholarship program, Davis Memorial Fund.

Other research projects