The great white shark looms large in our fears and imagination, but surprisingly little is known about it.
RNZ science presenter and wildlife expert Alison Ballance has swum with 15 varieties of shark in her career.
She has just released a book – New Zealand's Great White Sharks: How Science is Revealing Their Secrets about a ten-year project (which her partner Malcolm Francis co-led) to tag and track the great whites found around New Zealand.
When the project started, it was believed New Zealand'as great white sharks were 'stay at home' animals who spent their lives in our cool coastal waters, Ballance says.
They have mostly been studied around the seal colonies on Stewart Island and the Chatham Islands, where teenage great whites (and a few male adults) spend three or four months feeding on seals every summer.
Now, electronic satellite tags have heralded a "revelation and a revolution" in great white shark science – it turns out they're international travellers who spend more months of the year in the Pacific than around here.
Ballance says their explorations are probably about food.
"Summer is a good time here with the seals, then if you head off to the tropics, the humpback whales are all heading north to breed so maybe there'll be dead whales along the way, there might be some dead whale calves. There's huge boiling aggregations of fish in the tropics – some of the reef fish, things like tuna are hanging out in the tropics."
It remains a mystery how great white sharks navigate, but she suspects they use a combination of methods.
"Magnetic field lines on the earth, they might be following the topography, they might be following water masses, they can probably sense things about the temperature and the taste of water that we can't. The great white sharks, when the're doing those amazing ocean migrations, they're spending about two-thirds of their lives right at the surface, right in that top metre of water – so maybe they're actually navigating by the sun and the moon and the stars."
It's also unknown where they mate and give birth, but we do know about their unusual style of reproduction.
A litter of 4 to 12 shark pups are first laid as eggs in the mother's uterus and hatch inside there soon after. The gestation period is unknown (maybe a year and a half) but in that time the mother pumps out hundreds and thousands of unfertilised eggs which the baby sharks consume in vast quantities until their bellies protrude with egg yolk.
About halfway through the gestation, the mother stops producing eggs. The babies start absorbing the egg yolk and protein and develop a big fatty liver as their stomach slowly shrinks and is absorbed into their bodies. At birth, they are 1.2 - 1.5 metres long and immediately independent, very quickly learning to eat fish and other small sharks.