MASS-TRANSFER DURING LACTATION OF AN ICE-BREEDING PINNIPED, THE GREY SEAL (HALICHOERUS-GRYPUS), IN NOVA-SCOTIA, CANADA

Mass transfer during lactation was examined by serial weighing of mother-pup pairs in an ice-breeding population of grey seals, in the southern Gulf of St. Lawrence (c. 46 degrees N-c. 63 degrees W), Canada. Male pups (17.1 +/- 1.3 kg, n = 4) were significantly heavier at birth (P = 0.01) than females (14.6 +/- 1.4 kg, n = 9), and grew significantly faster until weaning (males: 2.7 +/- 0.6 kg/d, n = 45; females: 2.4 +/- 0.5 kg/d, n = 63, P = 0.04). At weaning, males (56.2 +/- 6.7 kg, n = 24) were significantly heavier (P = 0.01) than females (51.6 +/- 5.3 kg, n = 25). Lactation for both sexes lasted 14.9 +/- 1.4 days (n = 13). At parturition, adult females weighed 227 +/- 26 kg (n = 26). During lactation they lost 5.6 +/- 1.1 kg/d (n = 35). An analysis of carcass composition of six females collected during different stages of lactation showed that they utilized 61% of their fat reserves during lactation. Efficiency of mass transfer varied from 25.3% to 70.4% (49.3 +/- 10.8%, n = 35). Examination of stomach contents indicated that some ice breeding females consumed food during lactation. Our results in this ice-breeding population show that females invest more in sons than in daughters.