In these temperate seas,
corals are replaced by forests of seaweed.
In the summer,
giant kelp can grow a staggering foot and a half a day.
These waters may not support the diversity found in coral reefs,
but they boast a far greater volume of animals.
And a lot of fish means a lot of fish-eaters.
Dusky dolphins off the coast of Kaikoura in New Zealand's South Island
are so well fed that they can form superpods a thousand strong.
After their epic journey from the tropics,
the young bull sperm whales have finally made it.
Sperm whales dive deeper than any other whale.
They're drawn here by the fabulous wealth of deep-sea creatures,
even the giant squid that lurk in the depths of a vast underwater canyon.
To dive so deep and remain there for over an hour,
whales must spend around ten minutes filling their lungs and blood with oxygen,
much to the interest of a passing fur seal.
These young bulls will now spend another 15 years
bulking up in the nutrient-rich seas.
Only when they have become 30-tonne giants
will the largest predators on earth
finally return to the tropics to compete for a mate.