These are long, slender, streamlined whales with a flat head and mouth about six metres long. They have a slate blue head and upper body but a light underbelly. Their back and sides are faintly mottled. With a heart as big as a small motor car, ten tonnes of blood pumps around their bodies. Their biggest arteries are so big that a child could crawl through them.
Blue whales live between sixty to ninety years.
Pygmy whales are whales of the open sea. They swim in all the world oceans, migrating thousands of kilometres every year. In winter, they migrate to breed in tropical seas, and in summer and spring they visit the polar seas to feed. On their travels some pygmy blue whales pass New Zealand, a few swimming through Cook Strait on their way. They usually swim alone, but calves often accompany mothers.