Reproduction

How do whales, you know… do it?

The game of life consists of passing one's genes on to the next generation. Reproduction is therefore of prime importance for all life on the planet. How do whales do it? Though cetaceans live in water, they are mammals. The young are fed directly through the placenta as they develop in their mother's wombs. After birth they feed on mother's milk. In other words, apart from a few differences, they do it like we do. You want more details? To better explain the miracle of life for these marine animals, we must first present the two main actors, namely the male and the female.

Physical considerations

In the case of the killer whale, the male of the species has a long, straight, triangular shaped dorsal fin, while the female's is short and curved. In this example it is easy to distinguish between the sexes. However, the only way to visually differentiate gender for most other species of whales is by examining the genital slit. For the female, this slit is situated at the base of the belly, near the tailstock. The opening of the vagina and the anus are found within and it is therefore referred to as the genitoanal slit. On either side of this slit is a fold of skin that encloses a nipple. The male's penis retracts into a genital slit which is situated midway between the anal slit, at the base of belly, and the navel. Reproductive organs are therefore hidden within the animals' bodies. If males are so secretive, it is not necessarily because they are timid. Actually, it is a question of hydrodynamics; whales are long and slender. This allows them to slide more easily through the water. Try to imagine what would happen if the "family jewels" were not properly stored away within the genital slit. Nature has a way of taking care of "details".

The preliminaries

Before the two actors take to the stage to perform the act of life, intense competition may take place between males of the same species. This competition is sometimes confrontational; aggressive combat can break out where teeth, tailstock, tail, or other parts of the body are often used as weapons. This is true of the humpback whale, for example. Another competitive strategy among males is to produce the greatest quantity of sperm possible. As the females of these species may mate with more than one male, whoever produces a very large quantity of sperm increases his chances of inseminating the female. The combat is therefore of a more subtle nature, taking place as it does behind the scenes. This is the strategy used by the harbour porpoise. It explains why during the rut male harbour porpoise testicles can grow to a combined weight of 2 kg, which is pretty impressive for animal that weighs less than 60 kg! A human male equipped in the same proportions would have testicles weighing over 3 kg.

The female also has her say in the selection of a partner. Take the case of the sperm whale. Males of this species produce powerful clicks. Certain characteristics of these sounds are likely related to the animal's size. Using this as an indication, the female could then chose to mate with a larger male, proof that his genetic material, the only thing he will pass on to his progeny, is of good quality. As well as their demonstrations of force, all evidence leads us to believe that the long and complex songs humpback whales plays a role in the courtship behaviour of the males. A female that is not ready to copulate, either because the potential partner does not suit her or because she is not in a fertile period of her cycle, may turn her body in such a way as to bring her genital slit out of the water, rendering it inaccessible to the males. The female may also try to escape by changing her diving behaviour, or she may become downright aggressive towards a male that is too insistent and does not meet her criteria.

Intimate moments

Actual observations of mating are rare in the wild. Most available information concerning this topic comes from observations of species held in captivity, such as the bottlenose dolphin and the killer whale. According to observations made of these animals, mating can either take place belly to belly or turned on the side. Erection of the male's penis is the combined result of an increase in blood pressure in this region and muscular contractions. The penis can even be controlled by muscles, as if equipped with a homing device. During copulation, the vagina receives the male organ and then, of course, the sperm. The female's ovum is thus, with a little luck, fertilized.

The miracle of life

The baby will develop in its mother's womb and be nourished through the placenta. Gestation is generally between 10 and 12 months. For certain species, such as the sperm whale, killer whale and pilot whale, gestation can last up to 16 months!

Most often birth takes place tail first, but it can also occur head first. It is possible, however quite rare, that the female give birth to twins. When this occurs, it is highly unlikely that both offspring will survive. The newborn's energy requirements are so high that the female would have great difficulty adequately feeding both calves.

At birth, a humpback whale calf will have already grown to one third of the length and one twentieth the weight of its mother, which is similar to the proportions of a newborn human. However, a newborn Atlantic white-sided dolphin calf, a species found in the St. Lawrence, is much larger. It can be half the length of its mother and one-sixth her weight! As soon as the calf is born it is able to swim, breathe, produce sounds and nurse. The female takes care of the young. There is no known case of a cetacean male assuming this type of care.

Little whale becomes big whale

The young whale grows rapidly thanks to the rich composition of its mother's milk which is made up of between 20% and 40% milk fat, depending on the species! Blue whale offspring will grow by as much as 80 kg per day. The blue whale calf will leave its mother once it is weaned, seven months later … and 17 tonnes heavier! For many odontocetes (toothed whales) the cow-calf association lasts well beyond the nursing stage. For certain populations of killer whales, such as those residing in the waters around Vancouver Island, calves can spend their whole lives in the company of their mothers, within a family unit where the father is absent.

And the story begins again!

Female cetaceans may reproduce every two or three years on average. Or, as is the case of the harbour porpoises in the Bay of Fundy, they may reproduce every year. The age at which young cetaceans are able to reproduce varies from species to species. In the case of the blue whale, both the males and females reach sexual maturity around the age of 5 years. Male sperm whales must wait more than 20 years before trying their luck at the game of life.

In a nutshell, that is how whales do it. If you would like to know more, read how, for many species of whales, reproduction means a long, fabulous voyage of thousands of kilometres: Migration: Where do the giants go?