The killer whales that outsmart fishing boats

Narrator: The fishermen are waiting, and so are the killer whales. Concrete blocks take the bait down to 200 metres, because tuna swim very deep as well as fast. With the line paid out, the crew can only wait and hope, and watch the whales. A fish has been hooked.

Narrator: The sound of the winch is a signal to the waiting whales. The fishermen will have to work as fast as possible to bring in the line. The whales simply bide their time. By the time the fish nears the boat, all the fight has gone out of it. This is as easy a meal as a killer whale could hope for.

Narrator: The whales can strip the tuna in minutes. All that remains for the fishermen are leftovers. This piracy on the high seas doesn't do much for the whales' popularity, but this is just too good an opportunity for them to miss. These killer whales began stealing fish in this way around 30 years ago. Now, the culture has spread among all the members of two local pods. The fishing boats don't stand a chance.

Narrator: A six-tonne orca slaps its tail with awesome, destructive power. Under the water, tail slaps are used to stun the herring. Most are picked off by the orcas, and soon the water glitters with fish scales, as the orcas methodically consume the ball of fish.

Presenter: My team and I had been lucky enough to happen upon a pod of orca that were socialising. We went out in our sea kayaks and paddled alongside them. The orca were leaping out of the water, breaching, coming alongside me, and just rolling onto their side so they could look up at me as they came past. It was truly breathtaking. But then they went from this playful, supersized dolphin, which is essentially what they are, into full-on predatory mode. I've never seen an animal switch as fast as this, ever.

Presenter: They'd encountered a fully grown male Steller's sea lion: three-quarters of a tonne of flashing teeth. A serious predator in its own right. Just... just wow.

Researcher (Russia): We are right now with a pod of orcas, and I've just taken a picture of one orca that's been tagged. It means that it's one of those orcas that has been released here in the Russian Far East. That means that despite all the arguments from the captive industry, orcas actually can be released and safely returned into their natural environment, and live a happy life where they belong.

Narrator: Killer whales don't just target prey smaller than themselves. Off the coast of California, a grey whale and her baby are in serious danger. The grey whale calf is just a few weeks old. It's following its mother north towards the summer feeding grounds in Alaska. As they move beyond the trench wall, the grey whales lose their cover. Out in the bay, the killer whales are listening for that telltale sound: the breathing of a grey whale. Immediately, their behaviour changes. The killers close ranks.