MASS-TRANSFER EFFICIENCY BETWEEN HARP SEAL (PHOCA-GROENLANDICA) MOTHERS AND THEIR PUPS DURING LACTATION

We investigated the efficiency of mass transfer in lactating harp seals through serial measurements on individual mother-pup pairs during the whelping seasons of 1988 and 1989. We also compared the influence of longitudinal versus cross-sectional sampling on estimates of the efficiency of mass transfer. Among longitudinally sampled pairs, pups grew at an average rate of 2.3 +/- 0.5 (mean +/- S.D.) kg/d (N = 20). The concomitant mass loss by females averaged 3.1 +/- 0.8 kg/d (N = 19). The mean efficiency of mass transfer was 77.0 +/- 13.6% (N = 19 pairs). Estimates of pup growth and female mass loss from regressions of cross-sectional data were 2.0 kg/d and 3.1 kg/d, respectively. These values produce an estimate of 65% for the efficiency of mass transfer. Consistent with the high efficiency of mass transfer, harp seal females contribute less of their total body mass to nursing (c. 28%) than most other phocids examined. The resulting energy savings may be important for females of an ice-breeding species, which migrate a long distance shortly after weaning their pups.