NARRATOR: The migrating humpbacks
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.