MILK INTAKE, GROWTH AND ENERGY-CONSUMPTION IN PUPS OF ICE-BREEDING GREY SEALS (HALICHOERUS-GRYPUS) FROM THE GULF OF ST-LAWRENCE, CANADA

In this study we document growth, milk intake and energy consumption i n nursing pups of ice-breeding grey seals (Halichoerus grypus). Change in body composition of the pups, change in milk composition as lactat ion progresses, and mass transfer efficiency between nursing mothers a nd pups are also measured. Mass transfer efficiency between mother-pup pairs (n=8) was 42.5+/-8.4%. Pups were gaining a daily average of 2.0 +/-0.7 kg (n=12), of which 75% was fat, 3% protein and 22% water. The total water influx was measured to be 43.23+/-8.07 ml . kg(-1). day(-1 ). Average CO2 production was 0.85+/-0.20 ml . g(-1). h(-1), which cor responds to a field metabolic rate of 0.55+/-0.13 MJ . kg(-1). day(-1) , or 4.5+/-0.9 times the predicted basal metabolic rate based on body size (Kleiber 1975). Water and fat content in the milk changed dramati cally as lactation progressed. At day 2 of nursing, fat and water cont ent were 39.5+/-1.9% and 47.3+/-1.5%, respectively, while the correspo nding figures for day 15 were 59.6+/-3.6% fat and 28.4+/-2.6% water. P rotein content of the milk remained relatively stable during the lacta tion period with a value of 11.0+/-0.8% at day 2 and 10.4+/-0.3% at da y 15. Pups drank an average of 3.5+/-0.9 kg of milk daily, correspondi ng to a milk intake of 1.75 kg per kg body mass gained. The average da ily energy intake of pups was 82.58+/-19.80 MJ, while the energy built up daily in the tissue averaged 61.72+/-22.22 MJ. Thus, pups assimila ted 74.7% of the energy they received via milk into body tissue. The l actation energetics of ice-breeding grey seals is very similar to that of their land-breeding counterparts.