have only one objective now, the safe house of Mozambique.

It's a whale-birthing paradise far from the usual hunting

grounds of great white sharks.

Vulnerable baby whales can nurse, grow, and gain strength.

The adults have traveled 4,000 miles to safety.

The warm water and lack of predators

give their species the best chance of survival.

[whale singing]

It's a magical time.

The whales spend up to four months mating,

birthing, and nursing their young.

[soothing music]

This is their time to bond and interact.

But these adult whales have not eaten since they

left Antarctica months ago.

Their strength diminishes each day,

and the time is coming when all of the adults and calves

will have to swim the 4,000 miles back to Antarctica

to feed.

Now, after four months up in Mozambique,

they start this return migration down,

and that's when it's going to get really interesting.

Because at that stage, you're going

to have these weak whales, these whales that haven't fed

up enough that have been starved for the last four or five

months.

And as they go down, they're going

to be the ones that, I think, are really

vulnerable to attack by sharks.