FACTBOX-Five facts about sperm whales

(Reuters) - Sperm whales tend to stick to deeper waters, making them harder to research than most other animals. Here are a few facts scientists do know about the giants which hold many records within the animal kingdom:

- HOW BIG ARE THEY?

Males tend to be around 16 metres, but females are not much longer than 12 metres. At birth, they are all about 4 metres long, weighing roughly a tonne.

They have the largest heads, noses, and brains within the animal kingdom, and the most powerful natural sonars known.

- HOW MANY ARE THERE?

Commercial whaling, banned in 1986, decimated the populations of sperm whales. Estimates vary but Hal Whitehead from Canada's Dalhousie University thinks they number about 350,000, down from 1.1 million before commercial whaling.

- WHERE DO THEY LIVE?

Sperm whales are found all over the world, but usually in deeper waters. Sperm whales have some of the largest gender differences known, not just in size but also in the sexes' geographical segregation. When not mating, the males spend time in cold waters around the poles, while the females and calves stay closer to the equator.

- HOW LONG DO THEY LIVE?