Drifting away: implications of changes in ice conditions for a pack-ice-breeding phocid, the harp seal (Pagophilus groenlandicus)

Abstract

Harp seals ( Pagophilus groenlandicus (Erxleben, 1777)) required drifting pack-ice for birth, nursing, and as a resting platform for neonates after weaning. Data on the yearly location of whelping patches in the Gulf of St. Lawrence collected between 1977 and 2011 were combined with ice cover data (thickness and duration) to examine whether female harp seals actively select particular ice features as a breeding platform and to describe how these ice features have varied over the last 40 years at three spatial scales: the entire Gulf of St. Lawrence, the southern gulf, and the “traditional whelping area” within the southern Gulf. From our analyses, harp seals prefer the thickest ice stages available in the Gulf: grey–white and first-year ice. Lower than normal ice coverage years were more frequent for the required grey–white and first-year ice than for the total ice cover and less frequent at the “traditional whelping area” scale close to the northwestern coast of the Magdalen Islands than at the Gulf of St. Lawrence scale. The frequency of light ice years increased and the duration of the ice season decreased throughout the last decade. Our study showed that the temporal availability and the spatial distribution of the suitable ice are important when evaluating the effect of changes in ice conditions rather than overall ice extent.