True seals (a group that doesn't include the fur seal) belong to the family Phocidae. Seals lack ear flaps and the ability to rotate their hind flippers forward to walk on land, which sea lions can do. Instead they pull themselves forward by their fore flippers, dragging their hind flippers behind them, with an inchworm-like motion. In the water, however, they are amazingly graceful, using their hind flippers in a sculling motion to propel themselves while steering with their front flippers.
Some species are deep divers—the northern elephant seal dives regularly to approximately 2500 feet and stays under routinely for 20–30 minutes per dive.
Seals give birth to one pup each year, nursing for a brief, intense period (anywhere from one month to a mere four days), before abruptly weaning their fat offspring and returning to the sea to feed. In the majority of seal species, the mother does not feed while nursing, so she loses weight and needs to rebuild her blubber stores after weaning her pup.
The pup is left to learn to swim and to hunt fish and squid on its own, while living off fat stores. Guided almost entirely by instinct, the pup makes the transition from utter dependency to independence.
Male seals generally compete to control access to females and usually mate in the few days before the females return to sea after weaning her pup. The embryo will begin to develop, but then remain suspended in the womb (this is called delayed implantation), until a female has rebuilt her blubber stores. Gestation is therefore about nine months, although female seals give birth at almost exact one-year intervals.
Seals are found in all waters of the world, from the Arctic and Antarctic to temperate and tropical waters.
Updated Aug. 7, 2007
