The Blue Planet (2001) s01e08 Episode Script
Coasts
1 The coast - the frontier between land and sea.
This is the most dynamic of all the ocean habitats.
The challenge here is to survive change, extreme change.
Cape Douglas, on the most westerly Galapagos Island, totally unprotected from the massive rollers of the PacificÂ, and one of the roughest coastlines in the world.
The marine iguanas of the Galapagos are the world's only sea-going lizards.
Seaweed is all they eat, but doing so is a dangerous business.
The local crabs have become specially flattened, minimizing the effect of the pounding waves.
And the iguanas have huge claws to grip the rocks.
This seaweed really is fast food.
There are only a few seconds in which to grab a few mouthfuls before the next breaker comes pounding in.
Females feed only on the exposed rocks, but the larger males dive beneath the surface to reach the weed.
They go as deep as ten meters, for there, below the destructive waves, they find the best fronds.
Cold-blooded, they have to return to land after about ten minutes to warm up again in the sun.
Finding food is not the only challenge for coastal residents.
These rocky shores are hardly a safe place to lay their eggs.
Each year, the marine iguanas have to journey inland to find a more suitable one.
The females lay their eggs in burrows and leave them there to hatch.
To do that, they need nice soft sand.
Down at the water's edge, it was easy to escape danger in rocky crevices.
Up here, the females are dangerously exposed.
A Galapagos hawk.
The lizards don't give up without a struggle.
These hawks stay on the coast all year, but they are exceptional.
Most of the birds that frequent this frontier spend most of their time in or above the open ocean.
However, all seabirds have to come to land in order to lay their eggs.
And, after many lonely months spent searching the ocean for food, they have to re-establish social relationships.
Frigate birds display and exchange nest material.
Waved albatross dance.
The need to lay eggs on firm ground ties the albatross to the coast, but parental responsibilities are shared.
While one looks after the egg, the other can go off to feed.
The need to breed brings many different animals to the coast each year for a few weeks.
Male sea turtles spend all their lives at sea, but the females, like birds, must come to land to lay their eggs.
To do that, green turtles that live and feed off the coast of Brazil swim 1,500 miles to the tiny island of Ascension, that lies bang in the middle of the Atlantic Ocean.
How they manage to navigate with such accuracy and find this tiny lump of rock just seven miles wide is a mystery.
But, each year, up to 5,000 turtles manage to do so, and then, close to the coast of Ascension, they mate.
Traveling to and from Ascension and nesting can take six months.
Throughout the entire time, none of them feed at all.
After mating, a female has to leave her natural element and haul herself onto land.
She does so at night, laying three or four times at 15-day intervals.
After that, she swims back to the seas off Brazil.
She returns to this very same island throughout her life.
Remarkably, all the world's sea turtles return, year after year, to a few traditional breeding sites.
Crab Island in Australia is one of them.
This tiny two-mile long crescent of sand, provides nesting sites for half the population of one of the rarest sea turtles.
Flat-backed turtles are over a meter long, but they have to be careful- there are other giant reptiles here, too.
Salt-water crocodiles.
Every night throughout the year, there are flat-backs burying their eggs all along this stretch of sand.
Nine weeks later, and things are about to happen.
These eyes shining in the darkness belong to night herons.
As if from nowhere, hundreds of birds appear on the sand dunes.
Pelicans wait patiently.
Jabiru storks pace up and down.
Before long, they see what they've been waiting for.
Because these turtles lay their eggs throughout the year, the hatchlings emerge nightly in a steady trickle of beak-sized meals.
The pelicans' broad beaks allow them to dig out the hatchlings before the herons can spear them on the surface.
The surf may be hundreds of meters away and at least a third do not survive the journey.
It's not just the birds that take them.
Crocodiles, sharks and hungry fish are all waiting in the shallows.
In fact, only one in 100 hatchlings will survive to adulthood.
Another beach, another continent and a very special night.
In Costa Rica, a turtle has found a way of reducing these dangers.
When Ridley's turtles arrive to la y their eggs, they don't come in tens or hundreds, but in thousands.
In the next six days, around 400,000 females will visit this beach.
At the peak time, 5, 000 are coming and going each hour.
The beach gets so crowded, they have to clamber over one another to find bare sand where they can dig a nest hole.
40 million eggs are laid in these few days.
These turtles ensure that six weeks later, when their hatchlings emerge, it's not just a trickle.
It's a flood! On some nights, over two million hatchlings race down to the sea together.
With so many appearing simultaneously, the predators are overwhelmed.
Most of the turtles reach the sea safely.
Leaving the sea and emerging onto land is hard enough for turtles.
It's even harder for fish.
Each year, for hundreds of miles along the Newfoundland coast, capelin throw themselves onto the beaches.
At least a million tons of fish floundering out of the water - a real gift for scavenging eagles and gulls.
Odd though it may seem for the fish, the capelin, like the turtles, have also come out of the sea to breed.
The males are trying to fertilize the eggs that the females deposit in the sand.
Like the Ridley's turtles, they've synchronized their mass laying with the tide.
In a few days, it will be over.
Most of the capelin die, but only after they've left their eggs in the sand.
Other capelin populations lay their eggs in the ocean, so why do the Newfoundland fish spawn on land? It seems that eggs deposited on the beach are safer from predators and develop faster than in colder waters out to sea.
But, wherever they do so, the huge spawning shoals provide the concentration of food that seabirds need when THEY assemble to breed.
95% of the world's seabirds nest together, mostly in large spectacular colonies.
This is Funk Island, 40 miles off the coast of Newfoundland - an isolated rock crammed with breeding seabirds.
This was the last breeding ground for the flightless great auk, sadly now extinct.
Today, it's still the world's largest guillemot colony.
Over a million of them share this island with 250,000 gannets.
It's not the lack of suitable sites that causes seabirds to breed in such densities.
Here, in the North Atlantic, there's a wide choice of empty coastline the birds could use.
The key factor limiting seabird colonies seems to be availability of food in the surrounding ocean.
There are lots of hungry mouths to feed and a constant demand for fish.
Throughout the long summer days, at colonies like Funk, there's a continual stream of birds heading out to find food and returning with full crops to feed their young.
Gannets will travel up to 200 miles from the colony on a single foraging trip.
They are not fussy eaters and will take everything from tiny sand eels to herring.
Puffins, on the other hand, are particular about what they eat.
Because they can only fly short distances, they only nest where there is a good supply of food close by.
One such place is the Sea of Okhotsk in far eastern Russia.
This is the island of Talan.
Throughout the long Arctic winter it is encircled by ice.
But as spring approaches, that begins to break up, and seabirds that have wintered far to the south begin to return.
Its isolated position and steep cliffs make Talan a perfect nesting site.
The tufted puffins arrive first.
These are the Pacific cousins of our less spectacular Atlantic species.
Horned puffins soon follow.
In all, 14 different species return to Talan each spring.
In a few weeks, the silent cliffs come alive to the calls of four million breeding seabirds.
This is a multi-story avian city.
Assembling in these colonies, after having spent a largely solitary life at sea, provides the birds with the social stimulation that is the key to coordinating their breeding.
By nesting and laying together, they ensure that most chicks will leave the nest at the same time.
Like the turtles, this is the way they spread the impact of predators.
The world's largest eagle - Steller sea eagle - a third as big again as a golden eagle.
Throughout the summer, the eagles hunt in Talan's crowded colonies.
Riding on the updrafts, they patrol the cliff tops, looking out for any kittiwake that ventures too far from the rock face.
The huge eagle swoops with the aerial agility of a falcon.
Co-ordinated panic among the kittiwakes confuses their attacker.
But the eagle doesn't give up.
And it has got one.
Another kind of seabird on Talan has a particularly effective way of defending itself against predators, but it doesn't appear until an hour before sunset.
As if from nowhere, dense swarms of seabirds suddenly arrive offshore.
They've spent the day feeding far away where the sea ice has already broken up.
They are crested auklets, hardly bigger than starlings.
A million of them return to Talan each year to nest in its fields of boulders.
For the hour before sunset, the hillsides come alive with huge flocks of circling auklets, They're nervous.
No one wants to be the first to land.
Auklets are very social when they're together at the coast.
One advantage of nesting in such densities may be the chance to share information on feeding sites.
It also gives them the opportunity to court.
But, most importantly, there is safety in numbers.
Ravens and peregrines circle above the scree slope every evening.
By taking off together, the auklets hope to confuse the predators.
Eventually, their persistence pays off.
The birds that face the greatest challenge in coming to the coast to nest are surely the penguins.
Unable to fly, they have no alternative but to brave the immense waves.
Most penguins live in the southern ocean, and they have to accept being hurled about by the surf.
Whatever the weather, the penguin parents have to come back to feed their chicks.
A southern sea-lion bull.
He knows the penguins always use the same traditional landing beach.
Having braved the thundering surf, the penguins have to make a mad dash across open rock to their nests.
Despite his massive size and a body adapted for swimming, the bull chases the penguins for 40 or 50 meters across the rocks.
Having caught his penguin, the sea-lion carries it into deeper water, where, by violently thrashing the little body, he skins his meal.
The seas around the Falklands are some of the roughest in the world.
In spite of that, the southern ocean is home to millions of tiny seabirds hardly bigger than swallows - petrels.
Being so small, they're very vulnerable to the bad weather.
A storm can blow them miles off course and keep them away from their nests for days.
But these birds have developed an effective solution to the problem.
They lay a rather special egg.
Most birds' eggs, left exposed for even a few hours, will chill and never hatch.
But these eggs are different.
They can be left undamaged for several days without incubation while the parents struggle home through the storm.
Prions have also come up with a good way to avoid most predators.
They never come back to the coast until after dark.
These are thin-billed prions.
Their burrows honeycomb this Falklands hillside.
It's deserted in daylight, but as soon as it's dark and difficult for airborne predators to hunt, the prions return.
As soon as they land, they call.
The problem, of course, is finding your burrow among all the others.
He's listening out for his mate's call.
And down he goes.
The Alaskan coast.
It's spring, and the last of the winter storms is subsiding.
The plankton in this sea is in bloom again.
Just off shore, humpback whales have returned to feed.
For these huge animals, there's a real risk in coming into such shallow water, and each year, a good number of them pay the price.
It's an ignominious ending for an aging whale, but so much flesh will not go to waste.
A black bear emerges cautiously from the woods.
Visitors to the coast that don't come to breed, usually come to scavenge.
A whole range of animals exploit the enormous quantity of food that washes up every day on coastlines around the world.
But, like so much of the coast, the quantity of flotsam and jetsam is unpredictable.
Nobody can rely on it alone.
This carcass even attracted a shy pack of wolves, only too happy to anoint themselves with the scent of rotting whale.
It was months before the scavengers finally cleaned up all the meat on this huge and unpredictable gift from the sea.
Whales give birth to their young at sea, so can spend their entire lives there.
Other marine mammals - ones that are, in fact, distant cousins of bears - have to return each year to their ancestral home on land.
The high Arctic.
Here lives one of them - the walrus.
Walruses spend nearly all their lives at sea.
But each year, for a few weeks, they have to return to the coast.
They seek out isolated beaches like Round Island in the northern Pacific.
Suitable sites like this, free from bears, are so scarce that at times as many as 14,000 animals will cram themselves onto this one beach.
When they first emerge from the sea, the walrus are white.
As warm-blooded animals living in a very cold ocean, they conserve heat by keeping their blood concentrated in the core of their bodies.
On land, it's warm enough for them to allow their outer blood vessels to dilate.
That turns their skin from white to pink.
Now they can molt the outer layers of their skin, rubbing themselves up against the rocks.
But more than anything else, coming to land brings the walrus relief from having to spend energy maintaining body temperature in an icy-cold ocean.
Heat conservation, in fact, may be the primary reason so many sea mammals are forced to return to the land each year.
The world's coldest seas are in Antarctica.
Each spring, half the world's southern elephant seals return to the island of South Georgia.
Elephant seals have a particularly thick insulation of blubber that keeps them warm.
For them, breeding is the only reason to leave the sea.
With temperatures down to minus 20, and 100-mile-an-hour winds, It can't be comfortable on the beach.
But heat dissipates more rapidly through water than air.
So even in these conditions, their young, which at first don't have a thick coat of blubber, will be far warmer on the land.
Once the males are established on the beach, the females soon follow.
Within just ten days, the empty beach fills up with 6, 000 elephant seals.
Almost immediately, the females give birth to pups sired the previous year.
Their milk is very rich and the pups grow astonishingly quickly.
In just three weeks, they turn from thin bags of skin, to fat balls of blubber.
As soon as they've given birth, the females become sexually receptive.
Now the advantages of breeding in dense colonies become clear.
Females can choose from many males, while successful males can have access to lots of females.
But to gain that access and control a harem of females, the bull must be prepared to fight.
The larger the male, the louder the roar, the more likely he is to win.
When males are well matched, these bloody battles will last 20 minutes or more.
Eventually, the loser retreats into a stream already pink with his own blood.
These battles certainly help females select the strongest bulls, but they bring great dangers to the pups.
Each year, in the denser parts of the colony, a fifth of the pups are crushed to death.
This is why it may be better to mate at the edge of the beach close to the sea.
Less dominant males hide in the surf.
They are waiting to try and steal an illicit mating with females as they come and go.
This male knows he has been spotted by the big bull who claims all the females on this part of the beach.
Breeding in groups can bring advantages to pups as well as to adults.
Along the coast of Patagonia, southern sea-lions breed together in groups several hundred strong.
For the growing pup, these colonies act rather like a school.
The bonds developed here may be vital for the rest of their lives.
Sea-lions are social animals.
As adults and young forage together, they probably share information about good feeding sites.
Conditions could hardly be better for the growing youngsters.
As the tide goes out, it leaves a selection of sheltered pools.
Perfect places for learning to swim.
At high tide, it's easy for the pups to take their first experimental dips in the surf.
A killer whale.
These young pups have never seen anything like it before.
The whales, though, are very experienced.
Each year, this same group turns up along the coast at precisely the same time as the pups start to swim.
The whales need to surprise the pups, so they have stopped calling to each other, and keep silent.
Speed is everything.
The whales do not take pups that are out of the water, but their momentum can drive them up the beach and then there's real danger of getting stuck.
The whale has to thrash in this frenzied way to get off the beach.
Most of the pups are taken into deep water while still alive.
And there the whales, apparently, play with them.
Often, an adult whale is joined in the game by a youngster.
It may be learning how to grab a seal pup before it risks a drive up the beach.
Whatever the reason, the seal pup - still alive - is tossed back and forth for over half an hour.
Even when the pup is dead, the whales' sport is not completely over.
We can only speculate at the real reasons behind this extraordinary behavior.
But, for the whales, the hunting season is a short one.
Before long, the pups learn to stay clear of the water, and the whales become less successful.
After two weeks, they move on.
The killing season is over.
That's how it often happens along the coast.
Things are always changing.
They're never the same for long in this, the most dynamic of all the ocean's habitats.
This is the most dynamic of all the ocean habitats.
The challenge here is to survive change, extreme change.
Cape Douglas, on the most westerly Galapagos Island, totally unprotected from the massive rollers of the PacificÂ, and one of the roughest coastlines in the world.
The marine iguanas of the Galapagos are the world's only sea-going lizards.
Seaweed is all they eat, but doing so is a dangerous business.
The local crabs have become specially flattened, minimizing the effect of the pounding waves.
And the iguanas have huge claws to grip the rocks.
This seaweed really is fast food.
There are only a few seconds in which to grab a few mouthfuls before the next breaker comes pounding in.
Females feed only on the exposed rocks, but the larger males dive beneath the surface to reach the weed.
They go as deep as ten meters, for there, below the destructive waves, they find the best fronds.
Cold-blooded, they have to return to land after about ten minutes to warm up again in the sun.
Finding food is not the only challenge for coastal residents.
These rocky shores are hardly a safe place to lay their eggs.
Each year, the marine iguanas have to journey inland to find a more suitable one.
The females lay their eggs in burrows and leave them there to hatch.
To do that, they need nice soft sand.
Down at the water's edge, it was easy to escape danger in rocky crevices.
Up here, the females are dangerously exposed.
A Galapagos hawk.
The lizards don't give up without a struggle.
These hawks stay on the coast all year, but they are exceptional.
Most of the birds that frequent this frontier spend most of their time in or above the open ocean.
However, all seabirds have to come to land in order to lay their eggs.
And, after many lonely months spent searching the ocean for food, they have to re-establish social relationships.
Frigate birds display and exchange nest material.
Waved albatross dance.
The need to lay eggs on firm ground ties the albatross to the coast, but parental responsibilities are shared.
While one looks after the egg, the other can go off to feed.
The need to breed brings many different animals to the coast each year for a few weeks.
Male sea turtles spend all their lives at sea, but the females, like birds, must come to land to lay their eggs.
To do that, green turtles that live and feed off the coast of Brazil swim 1,500 miles to the tiny island of Ascension, that lies bang in the middle of the Atlantic Ocean.
How they manage to navigate with such accuracy and find this tiny lump of rock just seven miles wide is a mystery.
But, each year, up to 5,000 turtles manage to do so, and then, close to the coast of Ascension, they mate.
Traveling to and from Ascension and nesting can take six months.
Throughout the entire time, none of them feed at all.
After mating, a female has to leave her natural element and haul herself onto land.
She does so at night, laying three or four times at 15-day intervals.
After that, she swims back to the seas off Brazil.
She returns to this very same island throughout her life.
Remarkably, all the world's sea turtles return, year after year, to a few traditional breeding sites.
Crab Island in Australia is one of them.
This tiny two-mile long crescent of sand, provides nesting sites for half the population of one of the rarest sea turtles.
Flat-backed turtles are over a meter long, but they have to be careful- there are other giant reptiles here, too.
Salt-water crocodiles.
Every night throughout the year, there are flat-backs burying their eggs all along this stretch of sand.
Nine weeks later, and things are about to happen.
These eyes shining in the darkness belong to night herons.
As if from nowhere, hundreds of birds appear on the sand dunes.
Pelicans wait patiently.
Jabiru storks pace up and down.
Before long, they see what they've been waiting for.
Because these turtles lay their eggs throughout the year, the hatchlings emerge nightly in a steady trickle of beak-sized meals.
The pelicans' broad beaks allow them to dig out the hatchlings before the herons can spear them on the surface.
The surf may be hundreds of meters away and at least a third do not survive the journey.
It's not just the birds that take them.
Crocodiles, sharks and hungry fish are all waiting in the shallows.
In fact, only one in 100 hatchlings will survive to adulthood.
Another beach, another continent and a very special night.
In Costa Rica, a turtle has found a way of reducing these dangers.
When Ridley's turtles arrive to la y their eggs, they don't come in tens or hundreds, but in thousands.
In the next six days, around 400,000 females will visit this beach.
At the peak time, 5, 000 are coming and going each hour.
The beach gets so crowded, they have to clamber over one another to find bare sand where they can dig a nest hole.
40 million eggs are laid in these few days.
These turtles ensure that six weeks later, when their hatchlings emerge, it's not just a trickle.
It's a flood! On some nights, over two million hatchlings race down to the sea together.
With so many appearing simultaneously, the predators are overwhelmed.
Most of the turtles reach the sea safely.
Leaving the sea and emerging onto land is hard enough for turtles.
It's even harder for fish.
Each year, for hundreds of miles along the Newfoundland coast, capelin throw themselves onto the beaches.
At least a million tons of fish floundering out of the water - a real gift for scavenging eagles and gulls.
Odd though it may seem for the fish, the capelin, like the turtles, have also come out of the sea to breed.
The males are trying to fertilize the eggs that the females deposit in the sand.
Like the Ridley's turtles, they've synchronized their mass laying with the tide.
In a few days, it will be over.
Most of the capelin die, but only after they've left their eggs in the sand.
Other capelin populations lay their eggs in the ocean, so why do the Newfoundland fish spawn on land? It seems that eggs deposited on the beach are safer from predators and develop faster than in colder waters out to sea.
But, wherever they do so, the huge spawning shoals provide the concentration of food that seabirds need when THEY assemble to breed.
95% of the world's seabirds nest together, mostly in large spectacular colonies.
This is Funk Island, 40 miles off the coast of Newfoundland - an isolated rock crammed with breeding seabirds.
This was the last breeding ground for the flightless great auk, sadly now extinct.
Today, it's still the world's largest guillemot colony.
Over a million of them share this island with 250,000 gannets.
It's not the lack of suitable sites that causes seabirds to breed in such densities.
Here, in the North Atlantic, there's a wide choice of empty coastline the birds could use.
The key factor limiting seabird colonies seems to be availability of food in the surrounding ocean.
There are lots of hungry mouths to feed and a constant demand for fish.
Throughout the long summer days, at colonies like Funk, there's a continual stream of birds heading out to find food and returning with full crops to feed their young.
Gannets will travel up to 200 miles from the colony on a single foraging trip.
They are not fussy eaters and will take everything from tiny sand eels to herring.
Puffins, on the other hand, are particular about what they eat.
Because they can only fly short distances, they only nest where there is a good supply of food close by.
One such place is the Sea of Okhotsk in far eastern Russia.
This is the island of Talan.
Throughout the long Arctic winter it is encircled by ice.
But as spring approaches, that begins to break up, and seabirds that have wintered far to the south begin to return.
Its isolated position and steep cliffs make Talan a perfect nesting site.
The tufted puffins arrive first.
These are the Pacific cousins of our less spectacular Atlantic species.
Horned puffins soon follow.
In all, 14 different species return to Talan each spring.
In a few weeks, the silent cliffs come alive to the calls of four million breeding seabirds.
This is a multi-story avian city.
Assembling in these colonies, after having spent a largely solitary life at sea, provides the birds with the social stimulation that is the key to coordinating their breeding.
By nesting and laying together, they ensure that most chicks will leave the nest at the same time.
Like the turtles, this is the way they spread the impact of predators.
The world's largest eagle - Steller sea eagle - a third as big again as a golden eagle.
Throughout the summer, the eagles hunt in Talan's crowded colonies.
Riding on the updrafts, they patrol the cliff tops, looking out for any kittiwake that ventures too far from the rock face.
The huge eagle swoops with the aerial agility of a falcon.
Co-ordinated panic among the kittiwakes confuses their attacker.
But the eagle doesn't give up.
And it has got one.
Another kind of seabird on Talan has a particularly effective way of defending itself against predators, but it doesn't appear until an hour before sunset.
As if from nowhere, dense swarms of seabirds suddenly arrive offshore.
They've spent the day feeding far away where the sea ice has already broken up.
They are crested auklets, hardly bigger than starlings.
A million of them return to Talan each year to nest in its fields of boulders.
For the hour before sunset, the hillsides come alive with huge flocks of circling auklets, They're nervous.
No one wants to be the first to land.
Auklets are very social when they're together at the coast.
One advantage of nesting in such densities may be the chance to share information on feeding sites.
It also gives them the opportunity to court.
But, most importantly, there is safety in numbers.
Ravens and peregrines circle above the scree slope every evening.
By taking off together, the auklets hope to confuse the predators.
Eventually, their persistence pays off.
The birds that face the greatest challenge in coming to the coast to nest are surely the penguins.
Unable to fly, they have no alternative but to brave the immense waves.
Most penguins live in the southern ocean, and they have to accept being hurled about by the surf.
Whatever the weather, the penguin parents have to come back to feed their chicks.
A southern sea-lion bull.
He knows the penguins always use the same traditional landing beach.
Having braved the thundering surf, the penguins have to make a mad dash across open rock to their nests.
Despite his massive size and a body adapted for swimming, the bull chases the penguins for 40 or 50 meters across the rocks.
Having caught his penguin, the sea-lion carries it into deeper water, where, by violently thrashing the little body, he skins his meal.
The seas around the Falklands are some of the roughest in the world.
In spite of that, the southern ocean is home to millions of tiny seabirds hardly bigger than swallows - petrels.
Being so small, they're very vulnerable to the bad weather.
A storm can blow them miles off course and keep them away from their nests for days.
But these birds have developed an effective solution to the problem.
They lay a rather special egg.
Most birds' eggs, left exposed for even a few hours, will chill and never hatch.
But these eggs are different.
They can be left undamaged for several days without incubation while the parents struggle home through the storm.
Prions have also come up with a good way to avoid most predators.
They never come back to the coast until after dark.
These are thin-billed prions.
Their burrows honeycomb this Falklands hillside.
It's deserted in daylight, but as soon as it's dark and difficult for airborne predators to hunt, the prions return.
As soon as they land, they call.
The problem, of course, is finding your burrow among all the others.
He's listening out for his mate's call.
And down he goes.
The Alaskan coast.
It's spring, and the last of the winter storms is subsiding.
The plankton in this sea is in bloom again.
Just off shore, humpback whales have returned to feed.
For these huge animals, there's a real risk in coming into such shallow water, and each year, a good number of them pay the price.
It's an ignominious ending for an aging whale, but so much flesh will not go to waste.
A black bear emerges cautiously from the woods.
Visitors to the coast that don't come to breed, usually come to scavenge.
A whole range of animals exploit the enormous quantity of food that washes up every day on coastlines around the world.
But, like so much of the coast, the quantity of flotsam and jetsam is unpredictable.
Nobody can rely on it alone.
This carcass even attracted a shy pack of wolves, only too happy to anoint themselves with the scent of rotting whale.
It was months before the scavengers finally cleaned up all the meat on this huge and unpredictable gift from the sea.
Whales give birth to their young at sea, so can spend their entire lives there.
Other marine mammals - ones that are, in fact, distant cousins of bears - have to return each year to their ancestral home on land.
The high Arctic.
Here lives one of them - the walrus.
Walruses spend nearly all their lives at sea.
But each year, for a few weeks, they have to return to the coast.
They seek out isolated beaches like Round Island in the northern Pacific.
Suitable sites like this, free from bears, are so scarce that at times as many as 14,000 animals will cram themselves onto this one beach.
When they first emerge from the sea, the walrus are white.
As warm-blooded animals living in a very cold ocean, they conserve heat by keeping their blood concentrated in the core of their bodies.
On land, it's warm enough for them to allow their outer blood vessels to dilate.
That turns their skin from white to pink.
Now they can molt the outer layers of their skin, rubbing themselves up against the rocks.
But more than anything else, coming to land brings the walrus relief from having to spend energy maintaining body temperature in an icy-cold ocean.
Heat conservation, in fact, may be the primary reason so many sea mammals are forced to return to the land each year.
The world's coldest seas are in Antarctica.
Each spring, half the world's southern elephant seals return to the island of South Georgia.
Elephant seals have a particularly thick insulation of blubber that keeps them warm.
For them, breeding is the only reason to leave the sea.
With temperatures down to minus 20, and 100-mile-an-hour winds, It can't be comfortable on the beach.
But heat dissipates more rapidly through water than air.
So even in these conditions, their young, which at first don't have a thick coat of blubber, will be far warmer on the land.
Once the males are established on the beach, the females soon follow.
Within just ten days, the empty beach fills up with 6, 000 elephant seals.
Almost immediately, the females give birth to pups sired the previous year.
Their milk is very rich and the pups grow astonishingly quickly.
In just three weeks, they turn from thin bags of skin, to fat balls of blubber.
As soon as they've given birth, the females become sexually receptive.
Now the advantages of breeding in dense colonies become clear.
Females can choose from many males, while successful males can have access to lots of females.
But to gain that access and control a harem of females, the bull must be prepared to fight.
The larger the male, the louder the roar, the more likely he is to win.
When males are well matched, these bloody battles will last 20 minutes or more.
Eventually, the loser retreats into a stream already pink with his own blood.
These battles certainly help females select the strongest bulls, but they bring great dangers to the pups.
Each year, in the denser parts of the colony, a fifth of the pups are crushed to death.
This is why it may be better to mate at the edge of the beach close to the sea.
Less dominant males hide in the surf.
They are waiting to try and steal an illicit mating with females as they come and go.
This male knows he has been spotted by the big bull who claims all the females on this part of the beach.
Breeding in groups can bring advantages to pups as well as to adults.
Along the coast of Patagonia, southern sea-lions breed together in groups several hundred strong.
For the growing pup, these colonies act rather like a school.
The bonds developed here may be vital for the rest of their lives.
Sea-lions are social animals.
As adults and young forage together, they probably share information about good feeding sites.
Conditions could hardly be better for the growing youngsters.
As the tide goes out, it leaves a selection of sheltered pools.
Perfect places for learning to swim.
At high tide, it's easy for the pups to take their first experimental dips in the surf.
A killer whale.
These young pups have never seen anything like it before.
The whales, though, are very experienced.
Each year, this same group turns up along the coast at precisely the same time as the pups start to swim.
The whales need to surprise the pups, so they have stopped calling to each other, and keep silent.
Speed is everything.
The whales do not take pups that are out of the water, but their momentum can drive them up the beach and then there's real danger of getting stuck.
The whale has to thrash in this frenzied way to get off the beach.
Most of the pups are taken into deep water while still alive.
And there the whales, apparently, play with them.
Often, an adult whale is joined in the game by a youngster.
It may be learning how to grab a seal pup before it risks a drive up the beach.
Whatever the reason, the seal pup - still alive - is tossed back and forth for over half an hour.
Even when the pup is dead, the whales' sport is not completely over.
We can only speculate at the real reasons behind this extraordinary behavior.
But, for the whales, the hunting season is a short one.
Before long, the pups learn to stay clear of the water, and the whales become less successful.
After two weeks, they move on.
The killing season is over.
That's how it often happens along the coast.
Things are always changing.
They're never the same for long in this, the most dynamic of all the ocean's habitats.