大象传媒

The whales have been travelling non-stop now for about two weeks and have swum around 1,500 kilometres. So far it's been pretty much plain sailing for most of them, but all that's just about to change. The whales are approaching an area of maximum danger - not all of them will escape with their lives. This vast chasm is the largest underwater canyon on the west coast of North America, plunging down 2km. Down in the shadows lurks one of the ocean's top predators. They know the whales are coming and every year they gather here and wait. Every grey whale mother that migrates up this coast will eventually find herself here - Monterey Bay. And out there is the biggest threat that our grey whales are going to face in their entire journey. Here they have a choice: either they dart across the mouth as fast as they can, or they try and sneak around the coastline as quietly as possible in the hope that they'll avoid detection. If they get it wrong it could mean the death of their calves or even themselves. So, do you run, or do you hide? But what could possibly threaten an enormous 35-tonne whale? These could. A fraction the size of a grey whale, but killer whales hunt in packs and they're proper carnivores. These are the only predators the whales really have to fear. Killer whales will often pursue mothers and calves for hours until they're exhausted. But by taking the long way round, our mothers and calves can hide in a vast underwater forest. The water here is thick with kelp, which grows in the shallows around the edge of the Bay, a place that the killer whales will not venture. So by travelling through the kelp mothers and calves can avoid attack. Older, more experienced mums, like Scar, will know this and when she gets here she'll hide herself and her calf away in the kelp forest. Less experienced mothers may take the short cut, with possibly fatal consequences.