Whales' migration threatened

To the tourists watching a humpback whale frolic with her newborn calf in the tropical waters off Ecuador's coast near Puerto Lopez, the sight of enormous fins surfacing, tails flipping and blowholes spouting is breathtaking.

The same scenes can be found up and down the South American coast, from Puerto Piramides in Argentina to Cabo Blanco in Peru and Bahia Malaga in Colombia.

But to marine biologists, these huge mammals are not as carefree as they appear, as global warming is killing off their food and changing their age-old migratory routes.