How Many Blue Whales Are Left? Population and Recovery

How many blue whales were there before whaling?

No one counted blue whales before industrial whaling began, so earlier numbers are reconstructed from catch records and population models. The best-studied case is the Antarctic. A 2004 analysis by Trevor Branch and colleagues estimated that about 239,000 Antarctic blue whales lived there before exploitation, with a likely range of 202,000–311,000.

Worldwide, the IUCN Red List notes there were at least 140,000 mature blue whales as late as 1926, when catches were already rising fast. Compared with today’s 5,000–15,000 mature animals, that is a loss of roughly 90% or more.

How whaling nearly wiped out blue whales

For centuries, blue whales were too fast and too large for whalers in rowing boats. That changed in the late 19th century, when Norwegian whalers began using harpoon cannons fired from steam-powered catcher boats. In the 1920s, factory ships able to process whales at sea opened up the Southern Ocean, the richest feeding ground of all.

The scale of the hunt was immense. About 350,000–360,000 blue whales were killed in the Antarctic in the first half of the 20th century, and the peak season, 1930–31, saw roughly 30,000 taken. Around 11,000 more were killed in the North Atlantic, mostly near Iceland, and about 9,500 in the North Pacific.

By 1973 the Antarctic population had fallen to an estimated 360 animals, less than 0.2% of its original size.

When were blue whales protected?

Protection came in stages, often too late. Blue whales received some protection in parts of the Southern Hemisphere from 1939 and complete protection in the North Atlantic in 1955. This was extended to the Antarctic in 1965 and the North Pacific in 1966, when the International Whaling Commission banned all hunting of blue whales worldwide.

The ban was not fully respected at first. Soviet whaling fleets continued to kill blue whales and other protected species illegally into the early 1970s, and the true size of these catches only became public decades later. Today the blue whale is protected under international law, listed on Appendix I of CITES, which bans commercial trade, and covered by the U.S. Endangered Species Act.

Are blue whale numbers recovering?

Yes, in most places where they have been studied, but at different speeds:

• Antarctic: from about 360 in 1973 the population grew to about 1,700 by 1996, increasing by an estimated 7% a year on average. It is still only a few percent of its original size, and the Antarctic subspecies is listed as Critically Endangered.
• Eastern North Pacific: the whales that feed off California and winter off Mexico and Central America number roughly 2,000. A 2014 study estimated about 2,200 animals and suggested this population may be close to the number its habitat can support.
• North Atlantic: numbers are uncertain and probably no more than a few thousand. Sightings have increased in the central North Atlantic around Iceland and in the Norwegian Sea.
• Pygmy and other populations: pygmy blue whales of the Indian Ocean and South Pacific probably number several thousand, while trends for blue whales off Chile and in the northern Indian Ocean are poorly known.

Around South Georgia, where whaling stations once processed vast numbers of blue whales, the species was almost never seen for decades. Sightings and recordings of blue whale calls there have become more frequent in recent years, a sign of slow return.

Recovery is naturally slow. A female does not breed until she is roughly 5–15 years old and then has a single calf every 2–3 years. Compare the even more precarious situation of another great whale in How many right whales are left?

How do scientists count blue whales?

Counting a scattered, deep-diving animal across whole oceans is difficult, so estimates combine several methods:

• Ship and aerial surveys: observers record whales along set routes, and statistics are used to estimate how many were missed.
• Photo-identification: each blue whale has a unique pattern of mottling. By matching photos taken in different years, researchers can estimate population size with mark-recapture models.
• Acoustic monitoring: underwater microphones pick up the loud, low calls of blue whales across hundreds of kilometers, and each population has a distinctive song.
• Genetics: small skin samples reveal how populations are related and how much they mix.

Because each method has gaps, most estimates come with wide ranges, and figures for remote waters are rough.

What threatens blue whales today?

The biggest known threat today is collision with large ships. Off the U.S. West Coast, 17 blue whales were known or suspected to have been killed by ships between 1998 and 2019, and many more strikes probably go unnoticed because carcasses sink. Off southern Sri Lanka, one of the world’s busiest shipping lanes crosses a blue whale feeding area. Programs off California encourage ships to slow to 10 knots (about 19 km/h) in whale zones, and moving shipping lanes has been proposed elsewhere.

Other risks include entanglement in fishing gear, underwater noise from ships, military sonar and seismic surveys, which can disturb feeding, and pollution. Climate change may become the most important long-term threat, because it can shift or reduce the krill swarms that blue whales depend on.

Despite these problems, the overall trend is positive. The return of blue whales to areas where they were once hunted out shows that ending commercial whaling worked, even if full recovery will take many more decades. For a wider view of record-breaking giants, see the largest animals in the world.