Variation in sea ice cover on the east coast of Canada from 1969 to 2002: climate variability and implications for harp and hooded seals

There is growing evidence that global change and climate variability are affecting sea ice dynamics in northern and eastern Canada. Such variability could have serious consequences for harp seals Pagophilus groenlandicus and hooded seals Cystophora cristata, which congregate to whelp on ice every February and March in the Gulf of St. Lawrence and off Newfoundland. We combined a numerical and spatial analysis of weekly averages of ice data to examine the variability of ice cover in eastern Canada during February and March, 1969 to 2002. Sea ice cover varied cyclically in eastern Canada during that time and exhibited a period of light ice years between 1996 and 2002. Spring thaw generally results in a significant reduction of sea ice cover throughout much of the study area, although some regions exhibit increases associated with oceanographic phenomena. Heavy ice years correlate with positive spring North Atlantic Oscillation (NAO) conditions and an in-depth analysis of highly anomalous (+/-) years (1970, 1972, 1981, 1993 and 2001) revealed consistent spatial and numerical patterns in ice dynamics. During light ice years, a synchronous and dramatic reduction in sea ice cover occurred in the Gulf and off eastern Newfoundland in the first and second week of March, coinciding with peak pupping periods for harp seals. Light ice years and rapid reductions in sea ice represent unquantified risks for pagophilic seals. These include increases in neonatal mortality, changes in food availability for pups and, possibly, increased risk of epizootics due to crowding on whelping patches. The magnitude of these risks may increase if observed changes in climate reduce sea ice cover in eastern Canada as they have in the Arctic. Patterns in sea ice cover and NAO conditions can be incorporated into short- and long-term management schemes aimed at ensuring the sustainability of commercially exploited pagophilic seal populations.