Calving interval

In the latter half of the breeding season, calves and mothers can often be seen spending time in the shade of relatively quiet islands. In the 16 seasons from 1987 to 2002, 105 mother whales and 28 calves were identified. In the 16 seasons from 1987 to 2002, we identified 105 mother whales and 28 calves with their tail fins. These mother whales gave birth to 173 calves over the course of the months. Using the presence or absence of calves as a clue, we can use the year to year records of female whales giving birth to determine the calving interval. In the Hawaiian and North Atlantic groups, it is said that they usually give birth every two to three years. In the Ogasawara Islands, the average figure is once every 2.1 years. However, there were some cases where they gave birth for two or three consecutive years. It is said that there are age differences in the gestation cycles of female whales, and that whales that have been sexually mature for a certain number of years or so-called “experienced mothers”, are more likely to ovulate and give birth the following year, even though they are nursing their calves. This also seems to depend on the mother whale’s physical condition, the amount of food she takes at the feeding grounds, and other favorable environmental conditions that allow her to store up the energy to conceive immediately after giving birth.

Highest calving female

The most frequently identified calving female whale is O-40, which has been confirmed to have visited 10 of the 16 seasons between 1987 and 2002, and is known to have given birth to six calves.


Growth of the baby whales (calves)

When we compare the calves of each parent and child, we find that they range in size from small, wrinkled, grayish-brown whales that appear to have been born very recently, to large, dark-colored whales. This difference in size is also reflected in their differences in behavior. Smaller whales will raise their tail between their dorsal and caudal fins, but will sink or roll over, giving the impression that they are still learning how to raise their tail. We can also see them lounging on top of the mother whale. A slightly larger calf lifts its flukes, but it slips into the water. It is difficult to photograph the tail fin of such a baby whale, and most of the time we can only photograph the dorsal fin. However, if you succeed in photographing the tail fin that appears momentarily in the waves during its birth year, you can follow its growth and learn about the age of the humpback whale, which is usually impossible to determine from its appearance. In the 16 seasons between 1987 and 2002, the Ogasawara Marine Center identified the tail fins of 28 calves. Of these, the one with the best track record is O-288 (also known as Mochini); born in 1992, now 11 years old.

Mother whale, daughter whale, and grandchild whale

For example, the female whale O-46 has been seen for eight seasons so far, and has given birth to four calves. Of these calves, O-288, a.k.a. Mochini, was born around Ogasawara in 1992. Mochini gave birth twice, once in 2000 and  then in 2003. Mochini (O-288) gave birth to O-46’s grandchild, accounting for the three generations of parents and children, having a very high rate of encounters with humans, indicating that they have been coming to Ogasawara throughout the years.