The vast, mysterious ocean is home to the world’s largest mammals, whales, whose reproductive cycles and birthing processes are wonders of the natural world. Unlike fish, whales give birth to live young, a characteristic they share with land mammals. Observing these events offers a glimpse into the resilience and adaptability of these marine giants.
The Journey of Gestation
Whale reproduction involves complex mating behaviors, including vocalizations and physical displays, with some species undertaking migrations of thousands of miles to breeding grounds. Mating occurs underwater, often belly to belly, with both males and females mating with multiple partners. Once conception occurs, the female whale carries her offspring in her uterus.
The gestation period for whales varies by species, ranging from 9 to 18 months. Humpback whales are pregnant for about 11 to 11.5 months, while sperm whales and killer whales can have gestation periods lasting 14 to 18 months. During this time, the calf undergoes substantial growth and development.
Birthing in the Ocean
Whales travel to warmer, shallower waters to give birth, which helps the newborn conserve energy as it develops an insulating blubber layer. Birth occurs underwater and is a swift event, taking a few minutes to an hour. The calf is born tail-first, a position that prevents drowning by allowing the head to emerge last.
Immediately after birth, the newborn calf must reach the surface for its first breath. The mother whale assists by nudging her calf upwards, or lifting it on her jaw to help it break the surface. Other females in the pod also participate in helping the newborn take its first breath.
Early Life and Calf Care
Following birth, a strong maternal bond forms, and the mother dedicates months or even years to raising her young. Whale calves nurse underwater, accessing nipples concealed in the mother’s abdominal mammary slits. Whale milk is rich in fat, ranging from 13% to 53%, which is much higher than land mammals’ milk and enables rapid growth and the development of a thick blubber layer for insulation. A blue whale calf, for example, can gain approximately 80 kilograms (about 176 pounds) per day.
The duration of nursing varies by species; baleen whale calves nurse for 4 to 11 months, while some toothed whales, like sperm whales, nurse for 4 to 5 years, or even longer for beluga whales, up to three years. During this period, the mother protects her vulnerable calf from predators such as sharks and orcas. Calves learn survival skills, including swimming, diving, and foraging, by staying close to their mothers, benefiting from the mother’s slipstream to conserve energy.
Protecting Future Generations
Pregnant whales and their calves face human-induced threats in the ocean. Ship strikes are a leading cause of mortality for several whale populations, with vessels overlapping with whale habitats and calving grounds. Underwater noise pollution from shipping disrupts whales’ ability to communicate, navigate, and find food, impacting their sensory systems and causing stress.
Entanglement in fishing gear poses another danger, with cases of whales suffering injuries or death. Climate change also affects whale populations by altering their habitats and food sources, such as the availability of prey like Chinook salmon for killer whales. Conservation efforts focus on mitigating these threats, including implementing vessel speed limits, reducing ocean noise, and addressing chemical contaminants, which are particularly harmful to calves as they are transferred through milk.