WATER FLUX AND MASS GAIN DURING LACTATION IN FREE-LIVING RINGED SEAL (PHOCA-HISPIDA) PUPS

Three ringed seal (Phoca hispida) pups were used to calculate water flux and milk intake, based on mass increase and dilution of injected tritiated water. Biological half life of tritium in ringed seal pups was 130 +/- 17 h (mean +/- S.D.). The plateau level of the isotope indicating equilibrium with the body water was, in all cases (N = 8), reached before the first blood sample was collected after 0.5 h. Daily water flux in the pups was 62.9 +/- 21.5 ml kg-1. Estimated daily milk intake of 1103 +/- 388 ml milk resulted in a mass increase of 386 +/- 104 g. Neonates had a fat content of 4.75%, and a water content of 70.1% (N = 3). Corresponding figures for a pup close to weaning were 36.5% and 46.3%. Isotope dilution calculations of body water gave an overestimate of 1.6% compared with body water content from desiccation. Ringed seal milk was found to contain 38.1% fat, 9.9% protein, 2.3% lactose and 1% ash.