Blue whales mostly travel alone or in groups of 2-3. Larger groups of up to 60 whales have been reported and are probably associated with feeding grounds.
However, the blue whale has the most powerful voice in the animal kingdom and its low-frequency sounds can travel in deep water over hundreds, or even thousands, of miles. Under these circumstances, animals which may appear to us to be traveling alone may actually be in constant contact with one another.
At birth, a blue whale calf is the largest baby on earth: approximately 8m long and weighing about 4 tonnes. They grow at a rate of 90 kg per day and wean after 7-8 months, once they have reached about 15 m in length, and are able to follow the normal migration pattern alone. They reach sexual maturity at 5-10 years.
This growth rate is astonishing and is probably the fastest in the animal kingdom. From conception to weaning, it represents a several billion-fold increase in tissue in just over a year and a half.
Like other baleen whales, the blue whale has no teeth so it is hard to tell its age but scientists believe they live until at least 50.
Usually one calf is born every 2-3 years. However, recent evidence suggests that the inter-breeding interval is shorter than before whaling occurred, possibly to increase the growth rate of populations. Gestation is 10-11 months. Virtually nothing is known about the mating system.
The species dives for 10-20 minutes at a time and usually feed at depths of less than 100 m. A blue whale’s stomach can hold one tonne of krill and it needs to eat about four tonnes of krill each day – which amounts to around 40 million krill each day in the summer feeding season.
To eat, the blue whale expands its throat plates and takes in water and krill, then it pushes the water out through its baleen plates, swallowing the krill that has stayed inside its mouth.
Population & Distribution
Pre-whaling, there may have been more than 250,000 blue whales. But relentlessly pursued by 20th century whaling fleets, the species was nearly exterminated before receiving worldwide protection in 1967.
From 1904 to 1967, more than 350,000 were killed in the Southern Hemisphere. Thousands more are thought to have been killed by Soviet fleets during the 1960s and 1970s.
In 1931, during the heyday of whaling, an astounding 29,000 blue whales were killed in one season. In total, about 360,000 blue whales were killed in the 20th Century in the Antarctic alone.
Current population and distribution
The blue whale has a truly global distribution, occurring in all oceans except the Arctic, and enclosed seas. But despite this, they are one of the rarest of the whales, numbering between 10,000-25,000. Most biologists consider them to be among the most endangered of the great whales.
Only one population, in the eastern North Pacific off California, is showing real signs of recovery and currently numbers about 2,000 animals.
Some of the remaining blue whales are of a subspecies known as “pygmy” blue whales. As their name suggests, they are somewhat less gigantic than “true” blue whales. Until recently, they were thought to be confined to the Indian Ocean region but recent studies indicate they may be more widespread.
Blue whales prefer deeper ocean waters to coastal waters. Populations migrate towards the poles, into cooler waters, in the summer to feed. They migrate back towards the equator, into warmer waters, in the winter to breed. Because the seasons are opposite in the Northern and Southern Hemispheres, the net result of these movements is that the Northern Hemisphere and Southern Hemisphere stocks do not mix.
Like other large whales, blue whales are threatened by chemical and sound pollution, habitat loss, overfishing of krill, ship strikes and becoming entangled in fishing gear.
Climate change could also have a major impact on its food supply, since global warming and associated ocean acidification may impact krill populations.
In addition, frontal zones – critical whale habitats – are projected to move further south due to climate change. Frontal zones are boundaries between different water masses, where water can rise from the depths, bringing with it large amounts of nutrients that stimulate the growth of phytoplankton and support substantial populations of prey species for whales.
Blue whales would have to migrate further (perhaps 200-500 km more) to reach and feed at these food-rich areas where they build up reserves to sustain themselves for the rest of the year.
These longer migration paths could increase the energy costs of migration and reduce the duration of the main feeding season. As frontal zones move southward, they also move closer together, reducing the overall area of foraging habitat available
What is WWF doing?
WWF efforts in this area over the coming years will be directed towards increasing awareness of the need for blue whale conservation at the national and regional levels, and to create opportunities for local communities to be involved in, and to profit from, cetacean conservation initiatives.
The majority of WWF’s global conservation work to protect whales and dolphins takes place within the context of the International Whaling Commission (IWC).
WWF is also promoting the creation of marine protected areas (MPA) in whale habitats: such as the network of MPAs that WWF-Chile has been advocating for to protect foraging and nursing grounds of blue whales in Corcovado. In 2014, three protected areas covering 120,000 hectares were approved by the Chilean government.