DIVING BEHAVIOR OF LACTATING HARP SEAL, PHOCA-GROENLANDICA, FEMALES FROM THE GULF OF ST-LAWRENCE, CANADA

Diving behaviour of four lactating harp seal females was recorded using time-depth recorders. The females spent 20·6 ± 3·8% (X ± SD) of their time hauled out on the surface of the ice, 34·2 ± 2·5% of the time in the water in a surface position, and 45·2 ± 5·9% of the time diving. A total of 3701 dives were recorded with a mean duration of 3·2 ± 2·4 min. The maximum dive duration recorded was 13 min and maximum recorded depth was 90 m. Only 0·6% of the dives exceeded the estimated aerobic dive limit of 10·4 min. The mean duration of haul-out periods was 1·2 ± 2·3 h. The average time between haul-out episodes was 3·9 ± 1·5 h. The majority of the haul-out periods (86%) were only 20·8 ± 10·3 min long, indicating that in most cases females returned to the ice only to nurse their pups. Longitudinal mass records showed that the females were losing an average of 2·8 ± 0·8 kg daily while pups were gaining an average of 2·3 ± 0·4 kg/day. The average mass transfer efficiency was 86 ± 19%. This extremely high transfer rate, with a recorded maximum of 111% for one mother-pup pair, can only be explained by females consuming some food during the lactation period, which is consistent with the diving records obtained during this study, but in contrast to the general belief that in most phocid species females fast throughout lactation. © 1993 The Association for the Study of Animal Behaviour.