Humpback Whale Reproduction System

By Sarah Cruden

environment

Humpback Whales travel (by swimming, being an aquatic animal) from different coastlines to suit their certain needs, for example; feeding on tiny shrimp-like krill, plankton and small fish. During the year, Humpback Whales migrate twice to summer feeding grounds near poles to warmer winter breeding waters closer to the Equator.  Due to the inconsistent amount of food that is spread out through the many oceans they travel, it is by chance they find food everyday.
Humpbacks are nearly hunted to their extinction making them endangered. Humpback Whales were first protected as endangered animals in 1966. Currently, it is believed that 30,000 to 40,000 humpbacks are left or about 30 percent of their original population; this is due to the hunting of Humpbacks that weren't that long ago.

Humpbacks are powerful swimmers, and they use their massive tail fin (called a fluke) to propel themselves through the water and occasionally, lunging themselves out of the water.

These large creatures can grow to 14.6 to 19 meters long (size relative to a school bus) and weighing up to 40,000 kilograms.

Fertilisation

The same with all mammals, having a child involves internal fertilisation and cross fertilisation. The genitals of both sexes of the Humpback Whale are nearly identical in appearance. Apart from the female having a large bump known as the hemispherical lobe at the tail end of the genital slit and the distance between the anus and genital slit varying between the sexes. Even though the penis of the humpback male is two and a half meters long, it normally retracts within the body.
The process of fertilisation is not very different to humans, in some ways; although they have specific times of giving birth. In mature males, the weight of the testes and the rate of sperm increase during the breeding season and 'coincidentally' females go through ovulation at the same point. As ovulation approaches, the Humpbacks appear to possess a polygynous mating system, with males competing aggressively for access to females.

Once they have arrived to the winter breeding grounds, intense competition begins between the males. To win over the female they must fight or either sing. Once either whale has one the fight/song, the whale inserts his penis into the females opening and releases approximately 100 gametes.

There are no disadvantages apart from the idea of fighting. It is a very manageable and thought out process. The fighting can sometimes be very dangerous as they can get serverly hurt with bloody and bruised wounds.

Video showing Humpbacks mating


DEVELOPMENT

Development in a female's stomach lasts up 11 to 11.5 months, this means Humpback Whales use the method of viviparity. During that time, the embryo grows approximately 17 to 35 cm per month. Calves are born in the warm tropical waters and subtropical waters of  each hemisphere. Newborns are usually four to five meters long, and are suckled by their mothers for a period of about five months. The female's milk is very nutritive, containing high concentrations of fat, protein and lactose. There is no parental investment on the part of the male. Breeding usually takes place once every two years, but it may occur twice every three years. In the latter situation, lactation may last longer that five months. Development is done internally due to their surroundings and their movement. Since they travel a lot during the year, they cant be going back and forth to the where they have placed their fertilisted egg, that would be a waste of time. This way they can carry their young with them, providing them with good and correct amount of nutrients.

The advantages of this method of development is that the taking care of the embryo isn't high maitenance because it is developed in the mother meaning you dont have to come back to the one spot and care for it.

A disadvantage to this method is having to eat double the nutrients for yourself and the embryo.

parental care

Humpbacks are very patient when it comes to development of their calves, they wait 11 to 11.5 months for one calf. Once calf has been given birth of, they teach the baby to survive and adapt to the living styles of a whale. Seeming that the baby calves have quite a gap between siblings, they would be an only child; meaning easy access to a large amount of attention: k-selection. After calf grows up as an independant whale itself, it doesn't leave the herd so still to an old age they will be taken care of. There is a large amount of parental care because the it takes a long time to produce one calf. They would want to make the most of their time, putting all effort to the upbringing of a healthy calf.

The advantages of this method of parenting ensures that there calf will have a very healthy and good lifestyle.

intriguing facts

Unlike most creatures, Humpbacks are a specie of the baleen whale. This means that they don't have teeth to mush and breakdown their food. They aren't in need of breaking down food into smaller parts because they eat small shrimp-like krill and small fish which just easily goes down their throat. Instead, they have baleen. Baleen is a filter-feeder system inside the mouths of baleen whales. The baleen system works when a whale opens its mouth underwater and the whale takes in water. The whale then pushes the water out, and animals such as krill are filtered by the baleen and remain as food source for the whale. Baleen is similar to bristles and is made of keratin, the same substance found in human fingernails and hair.

Humpbacks have a unique way of communicating with one another: singing. Their are many different sounds they make that mean a variation of things. Humpbacks usually use this method of communication  towards sexual selections, for example; to attract a female to mate with.

An example of some whale sounds

flips

A variety of their most famous moves:

BREACHING

Jumping high out of the water and slapping as they come back down. This behaviour may be done to loosen skin parasites or just for fun.

TAIL SLAP

This is when the Whale slap its tail with full force into the ocean. The action of their tail slapping the water makes an intense sound and really shows off the size and strength of these amazing animals.

PEDUNCLE THROW

The whale converts its forward momentum into a crack-the-whip rotation, pivoting with its pectoral fins as it drives its head downward and thrusts its entire fluke and peduncle out of the water and sideways.

SKY-HOPPING

When a Whale pokes its head out of the water and takes a look around or having a breath of air. Usually lasts for about 30 seconds.

  Bibliography

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