Activity of lactating ice-breeding grey seals, Halichoerus grypus, from the Gulf of St Lawrence, Canada

Abstract

Abstract. The activity of seven lactating, ice-breeding grey seal females was quantified using time-depth recorders. The females spent an average of 72·2 ± 21·7 (SD)% of their time on the ice, 20·1 ± 16·7% in the water at the surface, and 7·6 ± 5·8% diving. A total of 2252 dives were recorded with a mean dive duration of 110 ± 82 s. The maximum recorded dive duration was 9 min 10 s. The females hauled out significantly more during dark hours (1900-0700 hours) than during light hours (0700-1900 hours). A significant negative correlation was found between increasing wind-chill index and decreasing numbers of females hauled out. The duration of haul-out periods and the intervals between them suggest that the pups nursed every 2-3 h. Average daily mass loss by mothers was 5·7 ± 0·4 kg. Average daily mass gain by pups was 2·4 ± 0·5 kg. The mean mass transfer efficiency was 0·44 ± 0·08. No correlation was found between maternal mass loss and pup mass gain among pairs or between mass loss or mass transfer rates and time spent in different activities by females. The lack of correlations between these variables, in addition to the dominant dive profile (where most of the dive time by the females was spent at the bottom), suggests that some ice-breeding grey seal females feed during lactation.