A. Gestation.
1. Harbor seals have a total gestation of about 9 to 11 months.
2. Gestation includes a period of delayed implantation: when the fertilized egg divides into a hollow ball of cells one layer thick (blastocyst), it stops growing and remains free-floating in the uterus for one-and-a-half to three months. The blastocyst then implants on the uterine wall and continues to develop.
3. Delayed implantation assures that the ensuing pup will be born when environmental conditions are optimal for its survival.
4. Implantation of the blastocyst may be triggered by hormonal changes at the end of the molting season.
B. Pupping season.
1. Although most pups are born in February through July, the pupping season varies widely among the regional populations.
2. Harbor seals of the northern Pacific population give birth from May to July.
3. Harbor seals inhabiting the coasts of British Columbia and Washington give birth from June to September.
4. Farther south, the pupping season becomes progressively earlier; in Baja California, the season is February and March.
C. Frequency of birth.
Females generally give birth to one pup each year. Multiple births are extremely rare, but twin fetuses have been documented.
D. Pupping.
Female harbor seals give birth on land, ice, or in the water near shore.
E. Pup at birth.
1. Pups are about 75 to 100 cm (29.5-39.4 in.) and weigh 8 to 12 kg (18-26 lb.).
2. Pups are well-developed at birth. Their eyes are open and they can swim and follow their mothers.
F. Care of the young.
1. Nursing.
a. A female harbor seal has two mammary glands on her lower abdomen.
b. Harbor seals have been observed nursing both on land and in the water.
c. A pup nurses for about one minute every three to four hours.
d. Pups nurse for about four to six weeks.
e. On average, harbor seal milk is about 45% fat, 9% protein, and 45.8% water, with traces of lactose (milk sugar). These figures may vary among individuals and may fluctuate throughout the nursing period. The extremely high fat content of the milk helps the pups more than double their weight by the time they are weaned.
Most harbor seal pups are born in February through July. Females nurse
their pups for about four to six weeks.
2. The female is an attentive parent during the nursing period. She noses the pup often. The pup may ride on her back, nip at her flippers, and chase her through the water.
3. Females recognize their own pups by vocalizations and by smell.
4. After her pup is weaned, the female shows no interest in the pup.
G. Pup growth and development.
1.A pup learns to catch and eat shrimp and bottom-dwelling crustaceans after it is weaned. Later, it learns to catch fish.
2. Pups do not wander far from adults.
During the nursing period, them mother is an attentive parent. The pup may
chase her through the water or even ride on her back.
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