Blue whales are the ocean’s “gentle giants.” These lightly mottled blue-grey whales with light grey or yellow-white undersides are the largest creatures known to have ever lived on Earth. Most blue whales range in length from 24-30 metres and the largest ever recorded was a gigantic 33.5 mt long. Female blue whales are up to 10 mt longer than males.
They can weigh up to 200 tonnes compared to the 6-tonne weight of an adult male African elephant. Even their tongues are heavier than the weight of elephants. A blue whale’s blood vessels are wide enough for a human to swim through. Bigger than the largest of dinosaurs, these jumbo-jet-sized giants inhabit the open ocean where they are found most frequently along the continental shelf edges and near polar ice.
The blue’s heart is the size of a small car and its beat can be detected two miles away. But that’s nothing compared to their calls. Blues are the loudest animals on earth and their calls can reach 188 decibels while a jet’s engine hit is just 140 decibels. Using very low-frequency sounds, a blue’s calls can carry for hundreds of km or even thousands of km underwater. Under these circumstances, animals which may appear to us to be travelling alone may actually be in constant contact with one another.
To maintain their immense size, the whales glide through clouds of krill, tiny organisms, only 1-2 cm long, resembling shrimp, sucking in great bellyfuls of water, and then straining the water back out through their baleen (pleats of fingernail-like material hanging from their upper jaws), trapping the krill as the water is ejected. There are a row of 300-400 baleen plates on each side of the mouth which are black in colour and range in length from 50 cm in front to 100 cm in the back.
A blue’s stomach can hold one tonne of krill and it needs to eat about four tonnes of krill each day – which amounts to around 40 million krill each day in the summer feeding season. A blue whale may pair up with another blue whale in their search for food. They may come together with more blue whales in areas with high concentrations of food, but they don’t form any larger groups with the others. Large groups of up to 60 whales have been reported. Otherwise, they are generally loners, rarely if ever forming pods – groups – like other kinds of whales.
Blues couldn’t eat a human even if they wanted to. They don’t have any teeth to chew meat up, and their throat is only about the width of one’s hand. That isn’t to say that they can’t do some damage. Their sheer size may cause accidental damage to boats or swimmers, and like any animal, if mommy whale thinks the baby is being threatened, there could be a giant-sized body-check.
Their general cruising speed has been measured at about 8 kmph. When they feed they’ll slow to about half that. When alarmed or playing, they can speed up to about 32 kmph.
Once a blue reaches between 5 and 10 years of age, it’s ready for reproduction. Scientists do not know much about the mating rituals of whales. Mating season usually starts in late autumn and carries on through to the end of winter. Once pregnant, the mommy-whale-to-be carries the baby inside her for close to one year.
When Junior finally plunges out into the water, he or she weighs about 2.7 tonnes, that is more than an adult rhinoceros, and can be 8 mt long, or the length of a super-stretch limousine. A single calf is produced every 2 to 3 years and from birth, each calf consumes up to 190 litres of milk each day, leading to a colossal weight gain of 90 kg per day in its first year of life.
The calf weans after 7-8 months, once it has reached about 15 mt in length, and is able to follow the normal migration pattern alone. This growth rate is astonishing and is probably the fastest in the animal kingdom. From conception to weaning, it represents a several billion-fold increase in tissue in just over a year and a half.
Big blues live about as long as humans, averaging between 80-90 years. Like other baleen whales, the blue whale has no teeth so it is hard to tell its age but scientists estimate a whale’s age by counting the layers in a dead whale’s earplugs, which are made up of a waxy substance. The oldest known blue lived to be 110 years old.
The blue has a global distribution, occurring in all oceans except the Arctic, and enclosed seas. But despite this, they are one of the rarest of the whales, numbering from 10,000 to 25,000. Most biologists consider them to be among the most endangered of the great whales.
Blue whales prefer deeper ocean waters to coastal waters. Populations migrate towards the poles, into cooler waters, in the summer to feed. They migrate back towards the equator, into warmer waters, in the winter to breed. Because the seasons are opposite in the Northern and Southern Hemispheres, the net result of these movements is that the Northern Hemisphere and Southern Hemisphere stocks do not mix.
By far, the greatest predator blues have ever known is man. While they were relatively safe in the earliest days of the whaling boom – their size and speed made them very difficult targets – the invention of the harpoon gun in 1864 led blue whale death-rate to skyrocket.
During the 20th century, the species was almost exterminated due to commercial whaling. The species has slowly recovered following the global whaling ban but it remains endangered and faces a number of serious threats including ship strikes, chemicals, and the impact of climate change.
In the pre-whaling era, there may have been more than 250,000 blue whales. But pursued by 20th-century whaling fleets, the species was nearly exterminated before receiving worldwide protection in 1967.
From 1904 to 1967, more than 350,000 were killed in the Southern Hemisphere. Thousands more are thought to have been killed by Soviet fleets during the 1960s and 1970s. In 1931, during the heyday of whaling, 29,000 blue whales were killed in one season. In total, about 360,000 blue whales were killed in the 20th Century in the Antarctic alone.