Since the beginning of September, the number of southern right whale (Eubalaena australis) cow-calf pairs in the bay has increased significantly compared to the last two months of our annual whale season. We have counted a total of about six cow-calf pairs in Plettenberg Bay, two of which are easily identifiable as a result of distinctive white markings. The one calf has a small white blaze on its back, while the other resembles its mother in having a white chin and white facial markings on its head. These calves have been delighting Ocean Blue guests with their exuberant displays as they breach and play alongside their mothers. The white-chinned calf, who is now about a month old, is especially playful and often lobtails and breaches alongside its mother. This calf has also taken a particular liking to swimming onto its mother’s back and then flopping over to the other side. During last week this particular calf approached our boat excitedly and swam around us before its mother decided it was becoming a bit too rambunctious and came to fetch it before swimming off with it.
Female southern right whales usually give birth to their first calf when they are 8 years old and at least 12.4 m long. The calves are born over a 118-day period, with a peak around late August, and after a gestation period of 12 to 13 months. The size of the calf at birth varies from 4.5 to 6 m, and is correlated with the size of its mother. For the next 3 to 4 months the calf will suckle milk from its mom in shallow, sheltered bays along the South African coastline and grow in length at an average rate of 2.8 cm/day. When the calf is about 8 m in length it is large enough to start its migration back south to the Subantarctic and Antarctic summer feeding grounds with its mother. It is unknown how long southern right whale calves are suckled for, but it is estimated that they suckle for a period of 6 to 12 months, as a few calves are still accompanying their mother at one year of age. Most females will give birth to a subsequent calf three years after the birth of their last calf.
Written by Danielle Conry
For further reading:
- BEST, P. B. 2007. Whales and dolphins of the southern African subregion. Cambridge University Press, Cape Town, South Africa.