The blue whale is the largest animal known to have ever lived, bigger than any dinosaur whose size has been reliably estimated. Yet this giant feeds on some of the smallest creatures in the sea.
Key takeaways
- Blue whales can reach around 30 metres in length and weigh well over 100 tonnes.
- They feed almost entirely on krill, filtering them from seawater.
- Their calls are among the loudest and lowest-pitched of any animal.
- Commercial whaling nearly wiped them out in the twentieth century.
- Populations have been recovering slowly since protection.
Size
The largest blue whales are thought to reach about 30 metres, roughly the length of three buses, and to weigh up to about 150 tonnes or more. Females are generally larger than males. A newborn calf is already about seven metres long and drinks hundreds of litres of rich milk each day, gaining weight very quickly. The size of the heart and arteries has often been compared to a small car or a large pipe, though precise comparisons vary and are best treated as illustrations.
Eating the smallest prey
Blue whales are baleen whales. Instead of teeth, they have rows of plates made of keratin, the same material as fingernails, that hang from the upper jaw. A whale gulps a huge mouthful of water with krill, small shrimp-like crustaceans, then pushes the water out through the baleen, trapping the krill. During peak feeding season, a blue whale may eat several tonnes of krill a day. Feeding is concentrated in cold, productive waters, and many whales migrate to warmer waters to breed.
Voices of the deep
Blue whales produce very low-frequency calls, many of which are close to or below the lowest range of human hearing, and they are among the loudest sounds made by any animal. Under the right ocean conditions, such sounds can travel long distances, possibly hundreds of kilometres, so whales may communicate over great ranges. Scientists use underwater microphones to study these calls and track populations. Shipping noise can interfere with whales' communication.
Diving and swimming
Blue whales usually swim at modest speeds but can accelerate when needed. They dive to depths of a few hundred metres to feed, and typical dives last around ten to twenty minutes. Between dives, they surface to breathe, producing a tall, narrow spout that can reach several metres in height.
Whaling and recovery
In the early twentieth century, whalers using explosive harpoons and steam-powered ships hunted blue whales intensively, particularly in the Southern Ocean. Hundreds of thousands were killed, and the global population fell to a tiny fraction of its original size. International protection came into force in the 1960s. Populations have since increased in some regions, though they remain far below historic levels, and the species is classed as endangered.
Modern threats
Ship strikes, entanglement in fishing gear, noise pollution and changes in krill availability linked to climate change all pose risks. Some countries have adopted measures such as shipping lane adjustments and speed limits in areas where whales gather.
Subspecies
Scientists recognise several subspecies or populations, including the Antarctic blue whale, the northern blue whale and the pygmy blue whale, which are somewhat smaller and found in parts of the Indian and Pacific oceans.
How a blue whale feeds
Blue whales are rorqual whales, with a series of pleats along the throat and belly. When feeding, a whale accelerates toward a dense patch of krill, opens its mouth very wide and engulfs a huge volume of water, which stretches the pleats like a balloon. The whale then closes its mouth and uses its tongue to push the water out through the baleen plates, trapping the krill. This lunge feeding is among the biggest bites in the animal kingdom, and a single gulp can hold more water than the whale's own body volume. Feeding is most efficient when krill are dense, so whales target productive areas.
Songs and communication
Male blue whales produce long, repeated low-frequency songs, and different populations have different calls. The calls are among the lowest-frequency sounds made by any animal, and some are below the range of human hearing. A mystery that fascinated the public was a whale that sang at about 52 hertz, higher than blue whales usually call, which was nicknamed the loneliest whale; its species has not been confirmed, and later recordings showed that similar calls were part of a wider pattern. Noise from ships and sonar can interfere with whale communication, and researchers study ways to reduce it.
Migration and life cycle
Many blue whales migrate between cold feeding grounds in summer and warmer breeding areas in winter, though their routes are not fully known. Females are pregnant for around ten to twelve months and give birth to a single calf that is about seven metres long. Calves drink rich milk for around six to seven months and grow quickly. Blue whales are thought to reach sexual maturity around age ten and may live for many decades. Their slow reproduction is one reason populations recover slowly.
Whaling and protection
Blue whales were hunted heavily until the mid-twentieth century. The International Whaling Commission protected blue whales in 1966, and a moratorium on commercial whaling took effect in 1986. Illegal whaling by some countries continued for years before it was exposed. Today, populations are recovering slowly in several areas, such as the northeast Pacific, but the Antarctic blue whale remains at a small fraction of its historical numbers.
Watching and studying whales
Scientists identify individual whales from photographs of the pigmentation pattern on their sides, a method called photo-identification, which lets them follow animals over many years. Tags attached with suction cups record dives, sounds and movements for hours or days, and drones can collect breath samples to study health and hormones. Responsible whale-watching follows rules on distance and speed, because boats can disturb feeding or cause fatal collisions.
Frequently asked questions
Are blue whales dangerous?
They are gentle filter feeders and pose no threat to people.
How long do they live?
Estimates suggest around 80 to 90 years, though this is hard to measure.
How many blue whales are there?
Estimates are uncertain, but some research suggests tens of thousands worldwide.
How big is a blue whale's heart?
A blue whale's heart is the largest of any animal and has been estimated at several hundred kilograms, roughly the size of a small car, though exact measurements are limited because few have been weighed. Its heartbeat can be very slow during deep dives.
How fast can a blue whale swim?
Blue whales usually cruise at about five to twenty kilometres per hour, and can swim faster in short bursts when needed, for example to escape danger or lunge at prey.
How long can a blue whale hold its breath?
Typical feeding dives last about ten to twenty minutes, though they may stay down longer on occasion. Between dives they return to the surface to breathe through blowholes.
Sources and further reading
Written by
FactNest Editorial Team
FactNest is operated by Muonix. The FactNest Editorial Team publishes general-interest explainers with AI-assisted drafting and illustrations. Contact contact@muonix.co for questions or corrections; we respond within 2 business days.
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