Blue Whale

The blue whale is the single largest animal that has ever lived on Earth — larger than any dinosaur, larger than anything in the fossil record. And it built that body by straining swarms of shrimp-like krill, each the size of a paperclip, out of the sea.

Overview

Blue whales are found in every ocean, roaming between cold, krill-rich feeding grounds near the poles in summer and warmer waters closer to the equator in winter, where they breed. They are rorquals — baleen whales with pleated throats — and the largest of that group by a wide margin. Populations are recognised in the North Atlantic, North Pacific, Southern Ocean, and northern Indian Ocean, and the little-studied pygmy blue whale of the southern hemisphere is a distinct subspecies.

The scale of it

Numbers struggle to convey a blue whale:

• Up to 30 metres long — roughly a basketball court.
• 150 tonnes or more — the mass of about 30 elephants.
• A heart the size of a small car, beating as slowly as twice a minute on a deep dive.
• Blood vessels a child could crawl through.
• A newborn calf is already 7 metres long and gains around 90 kg per day drinking its mother’s fat-rich milk.

The body is a smooth blue-grey, mottled so that from above it can look almost turquoise through the water — hence the name.

Feeding

Blue whales are lunge feeders. A whale accelerates toward a dense patch of krill, opens its jaws to nearly 90 degrees, and its pleated throat balloons out to engulf a volume of water and prey greater than the whale’s own body. It then closes its mouth and uses its car-sized tongue to force the water out through several hundred plates of baleen — bristly keratin combs hanging from the upper jaw — leaving the krill behind to be swallowed. A single lunge can net a whale half a million calories; it repeats the process for hours.

Because this is only worthwhile where krill are extremely concentrated, blue whales spend much of the year travelling between the few places and seasons where such swarms form.

Communication

Blue whales produce some of the loudest and lowest sounds of any animal — long, moaning pulses mostly below the range of human hearing. In the deep ocean sound channel these calls can travel for hundreds, possibly thousands, of kilometres, allowing widely separated whales to stay in acoustic contact across an ocean. Different populations have distinct call “dialects” that researchers use to tell them apart.

Reproduction and life cycle

A female gives birth to a single calf every two to three years after a pregnancy of about 11 months. The calf nurses for six to seven months, weaning once it reaches roughly 16 metres, and reaches full size and sexual maturity at around 10 years. Blue whales are thought to live 80 to 90 years or more.

Threats and conservation

The blue whale is listed as Endangered with an increasing trend — a species pulled back from the edge but nowhere near recovered:

• Whaling in the 20th century was catastrophic, removing about 99% of the global population before it was banned.
• Ship strikes are now a leading cause of death, especially where shipping lanes cross feeding areas.
• Entanglement in fishing gear, chronic ocean noise that masks their calls, and climate change — which is altering the timing, location, and abundance of krill — are the other major pressures.

Slow reproduction means recovery is measured in generations, but blue whale numbers are rising in parts of the North Atlantic and North Pacific, and sightings in some former hunting grounds are the highest in a century.