Reproduction of Blue Whales

MATING AND BREEDING:

     Females give birth to calves every two to three years. They remain pregnant for about one year before giving birth. When born, the blue whale calf is about 23 feet (7 m) long and weighs 5,000 to 6,000 pounds (2,700 kg). A nursing blue whale mother produces over 50 gallons (200 liters) of milk a day. The milk contains 35 to 50% milk fat and allows the calf to gain weight at a rate of up to 10 pounds an hour or over 250 pounds (44 kg) a day! At six months of age and an average length of over 52 feet (16 m), the calf is weaned. The blue whale reaches sexual maturity at around 10 years of age.

     Blue whale breeding occurs mostly in the winter to early spring while near the surface and in warm waters. The gestation period is about 11-12 months and the calf is born tail first (this is normal for cetaceans) and near the surface in warm, shallow waters. The newborn instinctively swims to the surface within 10 seconds for its first breath; it is helped by its mother, using her flippers. Within 30 minutes of its birth the baby whale can swim. The newborn calf is about 25 feet long (7.6 m) and weighs about 6-8 tons (5.4-7.3 tonnes). The baby is nurtured with its mother's fat-laden milk (it is 40-50% fat) and is weaned in about 7-8 months. Calves drink 50-200 pounds (23-90 kg) of milk each day. The mother and calf may stay together for a year or longer, until the calf is about 45 feet long (13 m).

Age to Maturity:

     In the Northern Hemisphere, females reach sexual maturity in 5 years at lengths of 21 - 23 m (69 - 75'). Males mature in slightly less time at just under five years and at slightly shorter lengths of 20 - 21 m (66 - 69'). (Wilson & Ruff 1999)

Length at maturity in the Southern Hemisphere for females is 23 - 24 m (75 - 79').

Gestation Period:

10 - 11 months.

Birth Season:

Calves are born in late fall and winter of the hemisphere they live in. 

Birth Rate:

    Usually one calf is born. Twins have been reported on rare occasions, but are extremely rare. (About 1% of births) The time between births is usually 2 - 3 years, although there is some indication that the current interval is shorter than before the populations were decimated by whaling, possibly as a density-dependent mechanism to increase the growth rate of the populations.