The blue whale (Balaenoptera musculus) is the largest animal ever to live. On average, adults weigh between 100 and 120 tonnes, and males are 23 metres long, while females are 24 metres. The whale’s heart weighs 2 tonnes and pumps about 270 litres with each beat. A child could fit inside the aorta (the blood vessel leaving the heart), and the main arteries are the diameter of sewer pipes. Even when the blue whale is under the greatest strain, its heart rate is no more than 20 beats a minute – compared with a human rate of 60–80.
In naming the blue whale, the 18th-century Swedish naturalist Linnaeus used the Latin word ‘musculus’ which means ‘a little mouse’. In giving this name to the largest animal in the world he may have been playing a joke. However, ‘musculus’ can also mean ‘muscle’ – perhaps a bit more appropriate.
On a diet of over 200 litres of milk a day, a whale calf puts on 90 kilograms daily, and by weaning time eight months after birth, it can weigh more than 20 tonnes. An adult was once found to have 1 tonne of food, mainly krill, in its stomach.
Blue whales are a mottled blue-grey and acquire a yellowish sheen from algae on their skins, explaining their common name ‘sulfur-bottoms’. Their tiny dorsal fin is set far back on the body. They have the loudest voice underwater of all animals, and their low frequency sounds travel hundreds of kilometres.
Dem bones, dem bones
When a blue whale was washed ashore near Ōkārito in 1908, the naturalist Edgar Stead and some friends retrieved the bones for the Canterbury Museum. Beset by sandflies, screeching gulls and the stench of rotting flesh, they attacked the whale carcass with knives, slashers, axes, shovels and a saw. The bones were then shipped to Lyttelton, and the public first viewed the 9-tonne skeleton in March 1909.
Population and migration
Blue whales were plentiful until the end of the 19th century because their speed (30 kilometres per hour) gave them the edge on non-motorised chaser boats. Hunted relentlessly in the 20th century, their numbers have plummeted. There are estimated to be fewer than 2,000 in the southern hemisphere. On their migration between the summer feeding grounds in the Antarctic and the equatorial waters where they spend the winter, blue whales used to swim through Cook Strait, and during the 19th and 20th centuries Tory Channel whalers would sometimes kill one. Blue whales still migrate past the New Zealand coasts, but are rarely seen close to shore.
Fin whales (Balaenoptera physalus), named for their prominent dorsal fin, are rare in New Zealand waters. The second longest of the whales at an average 20 metres, the fin whale has an asymmetrical colour scheme as its right jaw, but not its left, is white. It is believed that they live up to 80 years.
The fin whale produces the lowest frequency sound in nature – below the range of human hearing – but it can be heard by other fin whales thousands of kilometres away. In the 1960s, when United States navy personnel first heard the whales’ deep moans, they could not believe they were animal sounds.
The fin whale is also remarkable for its long migration, and its speed. It travels as far as 20,000 kilometres each year from the Antarctic to the tropics to mate and calve. Known as the ‘greyhound of the oceans’, it is noted for its stamina. One whale averaged 17 kilometres per hour over 3,700 kilometres.
The southern hemisphere population is estimated to be about 20,000, a fraction of the pre-whaling numbers. From the 1950s to the 1970s Soviet whalers killed 720,000 in the Southern Ocean region.