Reproduction
How do whales do IT?
Although cetaceans live under water, they are mammals all the same. The young develops in the mother’s uterus and is fed directly by the placenta and later, after it is born, by her milk. In short, with a few minor differences, whales do it… just like we do!
Built to purpose
In most species, the only fail-safe way to visually distinguish the sexes is to examine the genital slits. In females, it is located at the base of the belly. This is where the vaginal opening is found, immediately next to the anus. On each side of the slit, there is a fold of skin that conceals a nipple. The male has a genital slit into which the penis is retracted. It is located halfway between the anus and the navel. The reproductive organs are thus hidden inside the body: whales have a streamlined profile that allows them to glide through the water; imagine now the result if the “family jewels” were not so well “tucked away” inside the genital slit…
Courtyard foreplay
Before the two actors take the stage, an intense competition can take place between males of the same species. Sometimes, this competition takes the form of aggressive fighting, as in the case of the humpback whale. For blue whales, males race for a female, a race nicknamed “rumba”. In fact, each ejaculation of a blue whale could produce around 20 litres of sperm. The blue whale’s genital apparatus is proportional to its imposing size, which can reach about 30 metres. The average length of a blue whale’s penis is 2.4 metres. Each testicle weighs between 45 and 68 kg, the same weight as a harbour porpoise.
Another strategy consists of producing the greatest amount of sperm possible to increase the male’s chances of fertilizing his partner. This is what the harbour porpoise does, which is why, during the rut, the male’s testicles reach a combined weight of over 2 kg… Not bad for an animal that tips the scales at less than 60 kg! A man endowed in the same proportion would have testicles weighing over 3 kg.
The female also has her say: if she is not ready to copulate, she might turn her body so as to expose her genital slit out of the water and thus out of reach. The female may also attempt to swim away or might even become outright aggressive toward an overly zealous male who doesn’t meet her criteria.
A little privacy
Copulations are rarely observed in the wild or even in captivity. Based on these observations, mating can take place belly to belly or turned on the side. The erect penis can be guided using muscles, almost as if it were equipped with a homing device. During copulation, the vagina receives the male organ and thus the sperm. With a bit of luck, the female’s egg is fertilized.
The miracle of life
The fetus develops in the uterus of the mother, who feeds it through the placenta. Gestation generally lasts between 10 and 12 months, even 16 months in some species. Calves are most often born tail first. Though quite rare, the female may give birth to twins. The newborn’s energy needs are taxing and a female will struggle to provide for two. At birth, humpback whale calves will already have reached a third of their mother’s length and one-twentieth of her weight. Which is comparable to the proportions of a human baby. However, newborn Atlantic white-sided dolphins are much larger: half the length of the adult and one-sixth of its mass! Immediately upon birth the calf is able to swim, surface to breath, emit sounds and drink its mother’s milk. Young are looked after by the female.
Little whale grows up
The young whale grows quickly thanks to its mother’s rich milk, which has a fat content of 20 to 40%, depending on the species! A blue whale calf, for example, puts on 80 kg a day. It leaves its mother once weaned, seven months later… and 17 tonnes heavier! However, for many toothed whales, the bond between mother and her young lasts beyond nursing. In some killer whale populations, the young will even spend their entire lives with their mother, in a family unit in which the father is absent.
And the story repeats itself!
A female can give birth about every two to three years, sometimes even annually, as is the case for the harbour porpoise. The age at which young cetaceans can in turn reproduce varies from one species to the next. For blue whales, sexual maturity for both males and females is reached after about 5 years. Male sperm whales on the other hand must wait over 20 years before taking a shot at procreating.
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