Nature

The Arctic is rapidly changing.

And with this change comes a remarkable shift in power

at the top of the world,

as solid ice turns to open sea.

One iconic Arctic hunter

may soon have to give way

to the surprising invasion of another.

This is probably the most terrifying predator

since Tyrannosaurus Rex.

Stories have just started to emerge,

from those that live here,

of these changing fortunes.

For the first time,

Western science

and Inuit knowledge are combining

to witness and document the arrival in the Arctic

of the most successful ocean predator of them all.

Narrator: This is the Arctic as we know it.

An ocean locked in ice.

Everything that survives here is supremely adapted

to this frozen world.

Bowhead whales live here year round.

Wrapped in two feet of blubber,

they are insulated from water temperatures of 30 degrees.

The narwhal's smooth shape and lack of dorsal fin

allow it to swim easily among the ice floes.

Seal pups use the ice as a platform

for resting and being fed...

...enticing the largest

land carnivore on Earth

out across the frozen sea.

The polar bear.

All through the winter,

it stalks hunting grounds a thousand miles from land.

Without the ice,

the polar bear could not survive here.

The ice is home.

With a solid surface beneath them

and a strong sense of smell,

polar bears have a great advantage over prey

that sooner or later must come up to breathe.

It's the ice

that lets them close in on their quarry.

Attacking from above,

they smash through to get to seals hiding below.

Good hunting at this time of the year

is essential to surviving the lean Arctic summers.

All animals that live here rely, in some way, on ice.

It's not just the polar bear.

But ice is becoming a fragile player

on the Arctic stage.

This is

one of the fastest-warming regions on Earth,

and it's melting at a breathtaking rate.

Large parts of the Arctic that were once frozen all year

are now free of ice in the summer.

There are many opinions on how much this place is changing,

but it's well-documented that, in the last years,

there's dramatically more water and less ice each summer.

And without sea ice throughout the year,

polar bears are unable to hunt.

Hunger is forcing some bears to improvise.

In a desperate attempt at a meal,

they climb up steep slopes to get to thick-billed murre nests.

It takes a lot of energy to reach these birds,

and often there is no reward.

But this isn't just a story about melting sea ice.

On land, the effects of warming are also startling.

Just beneath the Arctic tundra

is a layer of permanently frozen soil.

Only mosses, lichens, and grasses can take root here.

But as temperatures increase,

parts of this frozen substrate are melting,

allowing trees to grow, sometimes with dramatic results.

In the far Western Arctic, the summer of 2008

produced the first forest fire ever recorded here.

This in a region where local Inuit dialects

don't even have a word for "forest fire."

In September 2012,

Arctic summer ice cover reached a record low.

The polar bear's world

is disappearing beneath its feet.

And as it does,

stories are emerging of the most powerful marine mammal

on the planet taking advantage.

For thousands of years,

the sea ice has kept this predator out of the Arctic.

Their immense dorsal fins can't break through the ice.

But increasingly,

there is no such barrier.

And this is no ordinary predator.

Armed with the second largest brain of all ocean mammals,

and with the ability to learn from one another,

killer whales -- also known as Orcas --

are remarkably intelligent and social hunters.

The Inuit were the first to witness

their arrival into Arctic waters.

Sam Omik and Gamailie Kilukishsak

can testify to the changing scene.

There are more killer whales now.

In the past, we would see them maybe once in the summer.

Now we see many more than that.

Inuit spend a lot of time hunting at sea,

and their firsthand experience

began to shed light on this marine predator.

We know they eat seals and narwhal.

And as they are predators like us,

they can probably eat anything they can get their hands on.

For Inuit who live here,

the summer Arctic has always been home to a natural bounty

that may now also be on the killer whale's menu.

The narwhal.

Narwhal spend all their lives in the Arctic,

navigating shifting ice packs and channels

both winter and summer.

This is one of the most mysterious animals

on the planet.

Known as the unicorn of the sea,

they have a single tusk that can reach up to 10 feet long.

Until recently, narwhal have faced

polar bears and human hunters.

But now a fearsome new presence has entered their waters.

I was hunting these narwhal,

and they were fleeing from some killer whales.

The killer whales were traveling fast and upside down,

and they breached the water chasing the narwhal.

When they got close to the shore

where the narwhal were,

they took bites out of two of the narwhal very quickly.

This is when I realized

that they are supreme hunters.

A report released in 2012

was the first to detail the recent arrival

of killer whales,

predators that were formerly unknown so far north

in Canadian waters.

That study was led by Steve Ferguson,

a marine biologist at Fisheries and Oceans Canada,

with a wealth of Arctic experience.

I've worked in the Arctic for over 30 years,

and over that time, I've seen a lot of changes.

For most scientists,

I think we looked at the Arctic

and knew that changes were happening

and wanted to understand how they were changing,

and we anticipated it to start from the bottom up.

Warming waters usually affect organisms

at the bottom of the food chain first,

which in turn impacts the diets of animals higher up.

But here, something else is also happening.

Changes are underway at the very top of the food chain

as access to Arctic waters opens up.

Killer whales have begun turning Arctic ecology on its head.

We really recognized the killer whale

as that top predator that, all of a sudden,

was making these huge changes in the Canadian Arctic,

and it was something we didn't really think about at the start,

but there it was, staring us in the face.

Steve's team became interested

in the firsthand reports of killer whale sightings

that were starting to reach them back in 2007.

Since then,

they've interviewed more than 100 Inuit hunters

in over 10 communities

and have opened up a gold mine of information.

Charlie Inuarak has been living in this part of the Arctic

all his life, and he's one of the region's best hunters.

Last year, we headed out on a hunting trip

to get some narwhal.

We were sitting at camp, and soon,

large numbers of narwhal began to arrive close to shore.

Soon after, we saw a pod of killer whales.

there were six or seven or of them.

We started to pack our gear,

and we followed the killer whales.

We knew we would catch narwhal

if we followed them.

Narwhal have always been key

to the survival of the Inuit.

Their skin contains large amounts of Vitamin C,

essential to the human diet.

For the last few summers,

Charlie has seen tantalizing evidence

that killer whales are also hunting and eating narwhal.

And this was backed up in the summer of 2013,

when Charlie's son managed to grab this footage

of killer whales in action.

By the time we got to where the narwhal were,

the killer whales had already killed some.

Over the next few days,

the killer whales stayed in the same area,

hunting and eating many narwhal.

This footage is probably the first time

killer whale predation on narwhal

in this part of the Arctic

has ever been captured.

What we saw was the bigger killer whales

eating the floating blubber.

The rest of the killer whales

were eating the narwhal from underwater.