The blue whale is the biggest mammal believed that ever existed, with a maximum verified length of 29.9 metres and a weight of up to 199 tonnes.

Other than mother-calf bonding, they are mainly lonely or assemble in tiny groups and therefore have no well-defined family system.

Till the late nineteenth century, the blue whale can be spotted in practically all of the earth’s oceans. Whalers drove it close to extinction until the International Whaling Commission prohibited all blue whale hunts in 1966. Blue whales were categorised as endangered by the International Union for Conservation of Nature in 2018. It is still threatened by a variety of challenges, including ship collisions, pollution, ocean noise, and climate change, as well as killer whale predation.

Ear plugs are the most reliable way to determine the age of a blue whale. Throughout their lifetimes, blue whales create earwax, which forms lengthy, multilayered plugs. Each accumulated bright and dark layer denotes a transition from fasting to eating while migratory. The number of layers is an indication of age since one set is put down every year. A pygmy blue whale’s maximum age calculated in this technique is 73 years.

Blue whales, on the other hand, exhibit fewer defined mobility patterns, including indications of year-round residence, partly or unequal migration, and unusual behaviours such as eating on breeding grounds. Data from individual satellite-tagged Eastern North Pacific blue whales indicate that they migrate at a speed of 7.4 km/h.

Blue whales consume krill via lunge feeder, a mass filter-feeding approach that includes speeding into a food patch at incredible speeds, widening the jaws 80–90°, and flipping the tongue, resulting in a huge sac.

This enables them to consume a huge quantity of krill-laden water, up to 220 tonnes at a time. With suction from the ventral pouch and mouth, they squeeze the water out of their baleen plates and digest the remaining krill.

A male blue whale will usually follow a female and it will battle off an invading male. Mating is considered to take place throughout the autumn and winter.

Female blue whales have calves each 2 – 3 years, depending on their bodily health and the length of their breastfeeding phase. A single calf of Antarctic blue whales is born at 7.0 metres in length and weighs 2.8–3 tonnes. In 2016, the first footage of a calf believed to be nursing was shot in New Zealand.

Killer whales are the major documented natural hazard to blue whales, however deadly assaults by killer whales have occurred on rare occasions. A sub-adult blue whale was attacked, killed, and eaten by killer whales off the south coast of Western Australia in May 2019.

Pollutants’ possible effects on blue whales are unclear. However, because blue whales graze near the bottom of the food chain, there is less risk of organic chemical pollutants bioaccumulating. Pesticides, flame retardants, and mercury were found in the earwax of a male blue whale killed in a clash with a ship off the coast of California.

An increase in anthropogenic underwater noise alters the acoustic environment and has an effect on blue whales. Aside from concealing blue whale transmission ranges, anthropogenic sound can elicit a variety of behavioural reactions.

Ship collisions are a major cause of death for blue whales, particularly along the West Coast of the United States, which has one of the highest concentrations of commercial ship activity in the world. Better predictive models of whale distribution, adjustments in sea routes, ship speed limitations, and seasonal and dynamic shipping lane management are all possible methods to reduce future ship strikes.

Due to their size and speed, blue whales were once challenging to hunt. Large-scale captures did not start until 1864, when Norwegian Svend Foyn developed the explosive harpoon cannon, which could be deployed on steam and diesel-powered ships. The number of blue whales slaughtered peaked in 1931, when approximately 29,000 were killed.

In 1966, the International Whaling Commission prohibited all killing of blue whales and granted them global protection. However, the Soviet Union continued to hunt blue whales illegally in both the Northern and Southern Hemispheres until 1973.

According to current climate change predictions, blue whale habitat will be drastically reduced. Furthermore, warmer seas may alter krill availability in a variety of ways, including vertical dispersion due to a deeper thermocline and increased stratification of the water column, as well as poleward shifts caused by the shrinkage of ideal habitats and changes in coastal upwelling. Blue whale prey, such as krill embryonic growth, hatching rates, and post-larval metabolic physiology, may suffer as a result of ocean acidification.

As of 2018, the worldwide blue whale population was predicted to be 5,000–15,000 adult individuals. Beginning in 1939, they were protected in parts of the Southern Hemisphere. Under the International Convention for the Regulation of Whaling, they were given total protection in the North Atlantic in 1955; this security was expanded towards the Antarctic in 1965 and the North Pacific in 1966. Iceland did not acknowledge the special protection of North Atlantic blue whales until 1960.

Blue whales are listed as endangered under the Endangered Species Act and are listed as deficient and critical under the Marine Mammal Protection Act. Blue whales are categorised as endangered by the International Union for Conservation of Nature.

They are also included in Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora and the Convention on Migratory Species of Wild Animals. Although there is little evidence on present availability trends for some species like Pygmy blue whales, others are seriously threatened.