Pinniped

Pinnipeds are a widely distributed and diverse group of semi-aquatic marine mammals.

Females have a postpartum oestrus that allows them to mate soon after giving birth. Delayed embryo implantation obviates the need to come ashore twice, once to give birth and again to mate. After giving birth, mothers suckle their young for a variable period. Phocid lactation varies from 4 to 50 days, whereas otarids lactate from 4 to 36 months. This reflects the fact that phocid feeding grounds tend to be far off-shore, so lactation is associated with maternal fasting. To compensate for the short lactation period, the fat content of phocid milk (45–60% fat) is higher than in any other marine mammal species. After lactation, most females migrate to feeding grounds for intensive foraging to recoup energy reserves. Otariid feeding grounds are generally closer to shore and mothers take foraging trips.

After the female returns from her first feeding trip the most important thing for her is to find her own pup out of the mass of other pups that are not her own.

Source: en.wikipedia.org/wiki/Pinniped - 09.04.2010