Three new hungry mouths arrive at the nearby river
a mother, accompanied by her two cubs.
The bear cubs don't seem to be very interested in fishing.
They've never known hard times.
They've spent the entire winter feeding on their mother's milk and their stomachs have never experienced hunger.
The mother, in contrast, has spent months feeding her young and needs to regain her strength for the coming winter.
With so much available food, the bears become less aggressive,
but an adult male is always dangerous.
Especially when there are cubs around.
The mother has smelt him and immediately goes on the alert.
The stranger is heading directly towards them, so the female decides to move off,
and when the male makes a sharp movement she flees with her offspring.
They will have to find a quieter river.
The flow of salmon is influenced by the tides.
At low tide, the current becomes stronger at the river mouth and this, combined with the reduced depth,
means it is not the best time to enter the water.
There are fewer salmon, and the predators take advantage to snooze or play on the beach revealed by the outgoing tide.
Six hours later the process is reversed,
and the sea returns to reclaim the land.
With the conditions in their favour, the indefatigable travellers again set off on their journey home.
A long time has passed since they descended these same waters on their way to the ocean.
Today, they are finally returning to their origins, to once again complete the cycle of life.
Thanks to their chemical receptors, the equivalent of the sense of smell in humans,
while still out at sea they detected the waters of their own rivers,
much like people differentiate one perfume from another.
And, guided by this, thousands of salmon dispersed across the Pacific Ocean
again gather at the same place they left years ago,
the river where they first came into the world.
Their bodies have now made the necessary changes.
Now, they can live in fresh water and are ready to face the next test,
the ascent up the river.
The jaws of the males have grown longer and have developed sharp, ferocious teeth
which they will use to fight for the females.
In some species, they have also acquired a characteristic hump.
But the most important change is that in their gonads, their sexual glands.
They have grown so much that they press against the stomach wall and prevent them from eating.
They will have to conquer the rapids, leap up waterfalls and escape from their predators without eating a single thing.
In the river they will have virtually no rest.
Even along the calmest stretches the current drags back any who do not struggle against it, so constant effort is required.
With no possibility of feeding, every lost minute reduces their precious reserves a little more.
And so the journey upriver becomes a race against time.
Along the river the salmon will establish their spawning grounds.
Some of them will spawn near the river mouth,
but others will have to travel hundreds of kilometres against strong currents
before they reach their destination.
And throughout the journey there will be predators trying to prevent them from ever reaching their goal.
The salmon are Alaska's particular staff of life, on which all other wildlife, directly or indirectly, depends.
Marine mammals, birds and land predators
rely on this torrent of proteins and carbohydrates which every year sweeps across the land.
Their enormous reserves, accumulated in order to survive for weeks without eating,
will pass directly to the bodies of their assassins.
Their only hope lies in sheer numbers.
While the predator is occupied with one victim,
others are able to escape and continue on their way.
This incredible nutrition explains why the bears here are the largest in the world.
Even within Alaska, those bears that live in the interior of the state and don't have access to this manna are much smaller.
Not every attempt is successful.
But at this time of year it's no problem if a salmon manages to escape.
After the first desperate days, and with their stomachs now full,
the bears have become much more choosy, and carefully select their prey.
The females, for example, are full of tasty eggs, and a real delicacy.
As the days advance, they reject more and more potential prey
and will accept only the most exquisite morsels offered by the river.
No one is more grateful for this attitude than the seagulls.
Their food is served up on a plate, without them having to make the slightest effort.
The number of dead bodies scattered along the river bank keeps on mounting,
but the bears, seemingly oblivious, continue the massacre.
As long as there are salmon in the river, they will not move far from the banks,
and at each high tide they again come down to fish.
Along the upper reaches, the shallower waters make fishing easier,
but the best places are those close to the river mouth.
Here, the salmon arrive in their prime, their bodies full of nutritious fat.
The bears know this, and so they concentrate downstream.
The upper reaches are left for the younger ones, who can't compete against the adults.
On occasions, a brave young bear decides to try his luck alongside the adults
but here each one has his own territory and anyone who tries to invade it is quickly repelled.