Blue whale guide: size, diet, reproduction - and just why blue whales are called blue

Why is a blue whale so big?

In the sea, the whales cruise easily, but on land an animal the size of a blue whale would be crushed by is own weight without the support of large, very heavy bones. As its body is supported by sea water, it’s possible for such an enormous animal to exist without heavy bones.

Whales have to be big – as a mammal living in the ocean, which gets much colder than land, they have to be big enough not to lose too much body heat to the surrounding water. Blue whales are the biggest, and can grow to 33 metres, and weigh 180,000kg if female, or 150,000 if male.

In addition, the ocean’s free-flowing environment allows for a vast food supply, enough to sustain a blue whale, to be eaten with ease. However, whales are limited in their size by their metabolism, which gets faster as they get bigger, effectively putting a limit on growth.

Is a blue whale bigger than Megalodon?

Yes, the largest blue whale ever recorded was 108 feet long, while the largest Megalodon specimen was only 58.7 feet long. Both were alive in the ocean during the Miocene Epoch, but the huge shark became extinct about 2.6 million years ago. The shark ate a diet of prehistoric whales, which may have included juvenile blue whales – but at a certain point, they would have become too large to be vulnerable.

Why is the blue whale called blue?

Blue whales are actually blue-grey, but they appear brilliantly turquoise in the water as they reflect the blue sky. They also have mottled markings on their sides that are unique to each whale, and which scientists can use to identify them.

Their undersides are light grey, or yellowy. In colder water, diatoms attach to the whales in vast numbers. These photosynthetic algae need a place to settle down, but in doing so, increase drag on the whale and colour it yellow with their bodies.

What do blue whales eat?

Blue whales feed almost exclusively on krill. During the summer months, they can consume as much as 40 million krill per day, and this is made possible by migrating to arctic regions, which have almost 24-hour a day sunlight during this time, leading to krill booms.Blue whales have overlapping plates of baleen hanging from their upper jaw instead of teeth. The whale takes in large volumes of water in its expansive throat, and as the water is expelled, the baleen fringes trap krill on the inside of the mouth.

How loud is a blue whale's song?

The song of a blue whale is painful for human ears, recorded at a cacophonous 188 decibels. Calls can be heard from up to 600 miles away, and sound travels faster underwater than in air. Because blue whales are solitary, it’s helpful for them to produce low-frequency, high intensity calls, that can be heard by whales many miles away.

Unlike humpbacks, both male and female blue whales sing, though females only sing in single notes while males sing in complex melodious tunes.

There is some evidence to suggest that populations of whales that are geographically separate produce distinct vocalisations. In a 2003 study, researchers described the most frequent sounds by North Atlantic blue whales, and compared them to blue whale sounds from other regions in order to draw conclusions.

Do blue whales migrate?

Yes, blue whales undergo a migration and must change their eating habits depending on the time of year. They spend the summer months feeding voraciously in order to stock up for the migration.

For the other half of the year, the whales are busy mating and calving in tropical or temperate waters, which are superb nursery grounds with few predators for juvenile whales, but which are bare of krill. Calves drink their mother’s milk as they migrate back to the poles, and adult whales fast.

How does a blue whale reproduce?

During the summer months, whales pair off, with males following a female for weeks on end. If a few males are competing for the attentions of one female, the whales initiate a race, possibly for the female to determine which suitor is more physically fit. Sometimes males engage in tail slashes and head ramming during these events.

Like other whales, blue whales produce vocalisations and they may have a reproductive function. Sometimes males call to each other when in pursuit of a female. Males also have a song that is used to court females.

Blue whales reach sexual maturity between six and ten years old, or when males are about 74 feet long and females are about 79 feet long. Calves are not born every year, but rather at intervals of two or three years, and blue whales have a gestational period of twelve months. When a whale is newly born, it is already seven metres in length, about the size of an elephant.

Is the blue whale endangered?

Sadly, yes. Blue whales were targeted by commercial whalers when equipment became advanced enough to catch them, and a single 90 foot blue whale could yield up to 120 barrels of oil. In 1930, 29,000 were reportedly killed in one season.

Now, blue whales are a protected species, but they are slow to recover. It is estimated that 99% of the world’s population of blue whales was eradicated during whaling. Pre-whaling populations were about 350,000, but now there are only about 15,000 blue whales in the world’s oceans.

Researchers have found that blue whales feed during the day and rest near the surface at night. This makes them more vulnerable to ship strikes in darkness, and studies are being carried out to get more information on whale behaviour so that conservation efforts can be implemented most effectively.

How long have blue whales lived on earth?

Present day blue whales are even larger than their prehistoric ancestors, and they are thought to have diverged from other prehistoric whale species during the Miocene epoch, when mammals were first evolving, possibly as much as ten and a half million years ago.

The life expectancy of a blue whale is 80-90 years old, with the oldest blue whale recorded at 110 years – similar to a human.