Harbor seal births are generally quite quick, usually too quick in the wild to catch on film!  The following photos were all taken on March 31, 2001, and document a breach (hindflippers first) birth of a Pacific harbor seal (Phoca vitulina richardsi).
(Photos courtesy of  A. Bohorquez, SFSU.  See also:  Bohorquez, A.S. 2002. Pupping phenology and haul out patterns of harbor seals (Phoca vitulina richardii) in San Francisco, California.  M.A. Thesis, San Francisco State University - Biology. 75 p.)

Harbor seals have a total gestation time of 9 to 11 months -- this includes a period of delayed implantation.  After the egg is fertilized and reaches the blastocyst stage, it stops growing and remains free-floating within the uterus for up to three months.  After this delay, the blastocyst implants into the uterine wall and continues to develop.

It is believed that delayed implantation helps to ensure that harbor seal pups are born at a time of the year which will be favorable to the survival and success of the new pup.

Females generally give birth to one pup per year; twins are very rare.  Due to the physiological requirements/energy demands of raising a pup, it would be almost impossible for a harbor seal mother to be able to support two offspring at once.

Harbor seal pups are born on land (or on ice in colder climates), or in shallow water close to shore.  Pups can weigh from 18 to 26 pounds (8 to 12 kg) at birth, and be 29 to 40 inches ( 75 to 100 cm) long.  Adult Pacific harbor seals can weigh up to 300 pounds (140 kg), though most will weigh less than that; average length is 5 to 6 feet (1.7 to 1.9 m).

Sometimes, seal pups are born on beaches accessible to people.  Mothers will sometimes leave their pups alone on land temporarily, while they go and forage for food.  A seal pup seen 'alone' on land should not be considered abandoned, as its mother may be waiting just offshore for a chance to retrieve her pup.  According to the Marine Mammal Center in Sausalito, CA, a seal pup's best chance for survival is to remain with its mother, as the seal mother's milk contains important antibodies that no substitute formula can provide.  If you see a pup that appears to be alone or in distress on shore, contact a marine mammal care facility in your area immediately.  Our "Things That You Can Do" page has a list of marine mammal rescue facilities on the west coast of the US.  If you can, try to keep onlookers, dogs, etc. as far away from the pup as possible.  Unfortunately, attempting to help the pup by taking it home, covering it with a blanket or approaching too closely will be doing more harm than good.

Pups are well developed at birth;
they can nurse and swim almost immediately after birth.

A harbor seal mother recognizes her pup by the sound of its call (pup calls sound like soft hoots or a "maaaa" sound) and by its smell.  Mother/pup pairs are often seen nuzzling nose to nose on land and in the water.  When a mother returns to the haul out site where she left her pup, her pup's call will help her locate and reunite with her pup.
 
 
 
 
 
 
 
 
 
 
 
 
 
 

   First Swim

Female harbor seals have two mammary glands on the lower abdomen.  Harbor seal pups will nurse on land and in water.  Pups stay with their mothers for roughly four weeks, and will gain a considerable amount of weight during the time they are nursing.  They may double in weight from the time they are born to the time that they are weaned.  Harbor seal mothers are protective of their pups, and typically do not tolerate other pups or adults getting too close.  However, we have documented several instances where an older unrelated pup will nurse off a seal other than its mother (in these instances, the mothers had only recently given birth and had not yet fully bonded to their own pups).
 
 
 
 
 
 
 
 
 
 
 

Sources:

A. Bohorquez, SFSU (photos).

Reeves, R.R. et al. (1992) The Sierra Club Handbook of Seals and Sirenians.  San Francisco:  Sierra Club Books.

and

The Marine Mammal Center, Sausalito, CA.