• Blue Whale

     

    Blue Whale

    The blue whale is the largest animal ever known to have existed. During the 20th century, the species was almost exterminated due to commercial whaling. The species has slowly recovered following the global whaling ban but it remains endangered and faces a number of serious threats including ship strikes and the impact of climate change.

    Physical description

    Blue whales are simply enormous with most ranging in length from 24-30 m. The largest ever recorded was a gargantuan 33.5 m long. Females are up to 10 m longer than males.

    And they can weigh up to 200 tonnes. Just to put that in perspective: an adult male African elephant weighs 6 tonnes!

    The blue whale’s heart is the size of a small car and its beat can be detected two miles away. But that’s nothing compared to their calls. Blue whales are the loudest animals on earth and their calls are louder than a jet engine: reaching 188 decibels, while a jet’s engine hit ‘just’ 140 decibels.

    Apart from their gigantic size, blue whales can be identified by their relatively small dorsal fin, a fairly rounded rostrum (anterior part of the skull), and approximately 90 ventral grooves, which reach the navel.

    They also have row of 300-400 baleen plates on each side of the mouth, which are black in color and range in length from 50 cm in front to 100 cm in back.

    Is the blue whale actually blue?

    Blue whales are a lightly mottled blue-grey, with light grey or yellow-white undersides.

    The yellowish ventral colouring is due to the accumulation of diatoms (microscopic, unicellular marine algae) in colder water, and has inspired the nickname “sulphur bottom whale”.

    Behaviour

    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.

    Life Cycle

    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.

    Breeding

    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.

    Diet

    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.

    Major threats

    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.

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