Reproduction and Growth
Lengths of gestation
The three species of baleen whale that hang in the Jacobs Family Gallery have pregnancies that last 11-12 months. Sperm whales typically gestate for 15 months. In general, most cetaceans have 10-13 month pregnancies, with some odontocetes like pilot whales and orcas having 16-17 month pregnancies.
Births tend to happen every 3-5 years. Twins are rare. The number of calves a female has over its lifetime depends on the species.
Calves are born tail first. This gives the flukes a chance to unfold, ensures that the blowholes are exposed to the water late in the delivery and that the heaviest part of the calf doesn’t come out first, and thus direct the newborn downward away from the mother.
Caption: (detail) Humpback Whales. Credit: Richard Ellis
Growth rate while nursing vs. growth rate while eating solid prey
Mysticetes nurse for 6-7 months, odontocetes for more than a year. Bottlenose dolphins for 3-4 years. Sperm whales often nurse for two years; juveniles as old as 13 have been found with milk in their stomachs, but are also eating prey.
Mysticete calves grow more quickly.
Marine mammal milk is high in fat (40-50%), high in protein (7-19%) and low in lactose (trace – 5%). Nursing episodes last short periods of time, anywhere from 15 seconds to 3-4 minutes, depending on species, because the calves need to surface frequently to breathe.
Calves of large species can double their length and quintuple (or more) their weight while nursing. A study published in 2012 estimates that North Atlantic right whales reach 76% of their maximum size by the time they are weaned. Fin and blue whales reach 70% of expected maximum size when they finish nursing.
Caption: North Atlantic Right Whale with fetus. Credit: Ashley Youngblood