For the first day or two of life, the newborn harp seal pup is a yellowish colour, the result of staining by amniotic fluid while in the womb. Yellowcoats are quite thin with a distinct head and neck, since they do not yet have the thick layer of insulating blubber found in older seal pups. The coat of the newborn harp seal, called the lanugo, is actually foetal hair which, in most mammals is shed in the womb prior to birth. The harp seal retains its lanugo for about two weeks.
Thin Whitecoat - Approximately 4 days
After two or three days, the pups lose their yellow colouration - it is either bleached by the sun or washed off by rain - and turn a pristine white. Feeding regularly on mothers milk, these thin whitecoats gain weight quickly, and grow stronger and more coordinated in their movements.
Fat Whitecoat - Approximately 7 days
Thanks to the high energy content of mothers milk (which contains more than 50% fat by the end of nursing), pups do not stay thin for long. In about a week, most pups have gained close to 14 kg (30 lbs). Nursing lasts for about 12 days and, during this time, the pups will grow about 2.2 kg (5 lbs) a day. More than half of this weight gain is stored as blubber.
Greycoat - Approximately 12 days
By the end of nursing, most pups weigh an average of 36 kg (80 lbs) or more. The dark spots of the developing juvenile coat can be seen growing underneath the longer white neonatal pelt. Weaning is abrupt and is not preceded by any change in nursing behaviour. The mother simply leaves, and never returns. Left to fend for itself, the pup continues to call for its mother for a few days, then becomes quiet and sedentary.