It’s that time of year again, when newborns start appearing in the warm waters along the Pacific coast – 500 kilogram, five metre-long newborn grey whales, that is. Calving season for this species is upon us and will continue through the first few months of the year. Soon after, mother and calf pairs will leave their calving grounds and travel north along the coast of B.C. to food-rich Alaska. Before these lengthy journeys begin though, life in those first few weeks and months will be full of learning and growth for the little ones.
In the beginning
Grey whales undertake one of the longest migrations of all mammals, travelling 15,000 – 20,000 kilometres, during a roundtrip from northern feeding grounds in Alaska to calving and breeding grounds in Mexico. Mating occurs in early winter during the last legs of the southward migration and after arrival at the breeding grounds off the Mexican coast. During this time, it’s not uncommon for mature grey whales to form large groups of mating adults, numbering as many as 20.
Steven Swartz Young grey whales are born in sheltered bays and lagoons off the coast of Baja California, Mexico.
After conception, gestation lasts approximately 13 months. Generally, females carry just one calf at a time, however, a deceased pair of conjoined grey whale twins was recently discovered. Most births occur at or near the pregnant female’s final destination: a sheltered bay or lagoon in Baja California, Mexico, although some calves make early appearances off the coast of California.
A grey whale’s “first steps”
Like most human babies, grey whale calves enter the world head-first (which is unusual for cetaceans). Initially awkward and uncoordinated, the calf is gently boosted out of the water by its mother, who may even support her newborn on her back while it takes its first breaths. Soon after, the calf will start to swim, its tail fluke quickly unfolding from a curled fetal position. Several small dimples are visible on the calf’s face and rostrum, free of the whale lice and barnacles characteristic of adult whales. Fetal folds, small creases formed as a result of the fetal position, are visible for the first part of a calf’s life, quickly disappearing as the little one gains blubber from nursing.
Charles Howell Grey whale calves are relatively free of the barnacles and whale lice that characterize mature individuals.
For the next few months, the calf will remain close to its mother, drinking 189 litres of milk containing 53% fat each day. This nutritious formula, which contains 13 times more fat than human milk, will help the calf grow rapidly and gain the strength needed to undertake one of the longest known mammalian migrations to Alaska, where mom can finally eat.
It’s not all warm and sunny
The journey northward can be a daunting one for mother and calf pairs. Several theories exist as to why whales travel long distances to mate and give birth, sacrificing food all the while. It may be worth the effort, as warm waters are thought to be less energetically costly for young calves. This means they can reserve energy that would be used to warm their bodies for other important things, like growing. Alternatively, some researchers believe grey whales seek lagoons and bays because they are safer. These areas are comparatively free of the number one predator facing young grey whales: Bigg’s (transient) killer whales. Given the chance to grow up in relative safety, these young animals are stronger and more robust when faced with predators on the journey north.
A Bigg’s (transient) killer whale tows a piece of grey whale flesh. Bigg’s killer whales prey on marine mammals, making them the number one threat to migrating grey whale calves.
The success rate for mother and calf pairs travelling to Alaska remains a mystery. An estimated 36% of calves do not survive the first leg of the northward migration to central California . Those that do make it will remain with their mothers for almost a year before separating – all in perfect time to start heading south again.
Early spring is the best time to see migrating grey whales in B.C. You can help researchers understand more about these whales by reporting any sighting of whales along our coast to the B.C. Cetacean Sightings Network.
References
Jenness, R. (1979, July). The composition of human milk. In Seminars in perinatology (Vol. 3, No. 3, pp. 225-239).
Perrin, W. F., Wursig, B., & Thewissen, J. G. M. (Eds.). (2009). Encyclopedia of marine mammals. Academic Press.
Swartz, S. L., & Jones, M. L. (1983). Gray whale (Eschrichtius robustus) calf production and mortality in the winter range. Rep. int. Whal. Commn, 33, 503-508.
Photo credit: Charles HowellGrey whale calves are relatively free of the barnacles and whale lice that characterize mature individuals.
Photo credit: Steven SwartzYoung grey whales are born in sheltered bays and lagoons off the coast of Baja California, Mexico.
Photo credit: Lance Barrett-LennardA Bigg's (transient) killer whale tows a piece of grey whale flesh. Bigg's killer whales prey on marine mammals, making them the number one threat to migrating grey whale calves.
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