0:00:04 > 0:00:10The power of the sun drives the seasons transforming our planet.
0:00:11 > 0:00:16Vast movements of ocean and air currents bring dramatic change
0:00:16 > 0:00:18throughout the year.
0:00:22 > 0:00:26And in a few special places, these seasonal changes
0:00:26 > 0:00:30create some of the greatest wildlife spectacles on earth.
0:00:37 > 0:00:42Here, on the western coast of North America in the spring of each year,
0:00:42 > 0:00:46one of the earth's greatest travellers comes home.
0:00:47 > 0:00:51Over half a billion salmon in the Pacific Ocean
0:00:51 > 0:00:53start on a 3,000 mile journey,
0:00:53 > 0:00:56returning to spawn in the rivers where they were born.
0:01:02 > 0:01:05Travelling deep into the continent,
0:01:05 > 0:01:09these fish will not only provide food for millions of animals...
0:01:14 > 0:01:19..they will also bring life to one of the richest habitats on Earth.
0:01:45 > 0:01:48The coast of British Columbia
0:01:48 > 0:01:52and Alaska is rimmed by spectacular mountains.
0:01:56 > 0:02:00Although it will be months before the salmon enter the rivers
0:02:00 > 0:02:02below these frozen peaks,
0:02:02 > 0:02:06one species that has spent the winter sleeping up here
0:02:06 > 0:02:09is already anticipating their return.
0:02:13 > 0:02:19In January, snug in their dens, the females have given birth
0:02:19 > 0:02:22and now the family is beginning to stir.
0:02:40 > 0:02:42Grizzly bears.
0:02:46 > 0:02:52Whether the cubs will live or die depends largely on one key event...
0:02:52 > 0:02:53the salmon run.
0:02:53 > 0:02:56For the next five months, the bears will be focussed
0:02:56 > 0:03:00on making their appointment with the returning salmon.
0:03:19 > 0:03:23Surviving the first year is hard.
0:03:23 > 0:03:27Half of all grizzly cubs don't make it.
0:03:40 > 0:03:43Throughout Alaska and British Columbia,
0:03:43 > 0:03:48thousands of bear families are emerging from their winter sleep.
0:03:50 > 0:03:52There is nothing to eat up here,
0:03:52 > 0:03:56but the conditions were ideal for hibernation...
0:03:57 > 0:04:01..lots of snow in which to dig a den.
0:04:05 > 0:04:09To find food, mothers must lead their cubs down to the coast,
0:04:09 > 0:04:12where the snow will already be melting.
0:04:17 > 0:04:22But getting down can be a challenge for small cubs.
0:04:50 > 0:04:55These mountains are dangerous places, but ultimately,
0:04:55 > 0:05:00the fate of these bear families - and, indeed, that of all bears
0:05:00 > 0:05:03around the North Pacific - depends on the salmon.
0:05:05 > 0:05:10Right now, those salmon are more than 2,000 miles away.
0:05:15 > 0:05:17After four years at sea,
0:05:17 > 0:05:23half a billion Pacific salmon are going home - back to freshwater,
0:05:23 > 0:05:27to lay their eggs in the rivers where they themselves were hatched.
0:05:38 > 0:05:44How the salmon manage to find their way back home across the open ocean
0:05:44 > 0:05:46is still largely a mystery.
0:05:47 > 0:05:50It has only recently been discovered
0:05:50 > 0:05:54that a salmon's brain contains small particles of iron
0:05:54 > 0:05:59that, like a compass, help it steer the magnetic lines of the earth,
0:05:59 > 0:06:01showing them exactly where to go.
0:06:21 > 0:06:26For many of these salmon, that destination is here,
0:06:26 > 0:06:29along the western coast of North America, in British Columbia.
0:06:36 > 0:06:40They are making their way back to their birthplace,
0:06:40 > 0:06:44in one of its many freshwater rivers and streams.
0:06:47 > 0:06:51Here, amongst the network of lakes and waterways,
0:06:51 > 0:06:56lies the largest expanse of temperate rainforest left in the world.
0:06:59 > 0:07:03It stretches from southern British Columbia to Alaska.
0:07:11 > 0:07:15It is one of the most fertile landscapes on the planet.
0:07:27 > 0:07:29The temperate rainforest
0:07:29 > 0:07:33supports even more life than its tropical counterpart.
0:07:38 > 0:07:43For thousands of years, salmon have returned to this country
0:07:43 > 0:07:45because of the abundance of one element -
0:07:45 > 0:07:47fresh water.
0:08:12 > 0:08:15This is some of the purest water in the world,
0:08:15 > 0:08:18thanks to these forests.
0:08:32 > 0:08:35Where the forests are still undisturbed,
0:08:35 > 0:08:40the soil, held by millions of tree roots, filters the water,
0:08:40 > 0:08:43keeping the rivers flowing clean and pure.
0:08:53 > 0:08:57In May, grizzly bears come down to the coast
0:08:57 > 0:09:03to find something to eat while they await the arrival of the salmon.
0:09:03 > 0:09:06This is where spring arrives first.
0:09:14 > 0:09:18The cubs, still feeding on nothing but their mother's milk,
0:09:18 > 0:09:20have grown considerably.
0:09:24 > 0:09:30But it has been six months since their mother had anything to eat.
0:09:39 > 0:09:43Now they need other food, and the search for it
0:09:43 > 0:09:45can lead them into danger.
0:09:49 > 0:09:52Some males will try to kill cubs.
0:09:56 > 0:09:59The breeding season has begun,
0:09:59 > 0:10:03and big males are here, looking for females.
0:10:19 > 0:10:22But at least there is something to eat here,
0:10:22 > 0:10:26even if it is only grass and sedges.
0:10:28 > 0:10:32These greens, in fact, can keep them going for months, but they will need
0:10:32 > 0:10:35something more nutritious if they are to put on enough fat
0:10:35 > 0:10:38to enable them to survive the next winter.
0:10:44 > 0:10:49In some places along the coast, bears find much richer food.
0:10:52 > 0:10:57It's buried, but bears have an extremely acute sense of smell
0:10:57 > 0:11:01and can sniff out a meal even if it is beneath the wet sand.
0:11:07 > 0:11:08Clams!
0:11:16 > 0:11:21It is not only bears that are drawn to the coast in search of food.
0:11:26 > 0:11:30There are more than 2,000 grey wolves in the Great Forest.
0:11:34 > 0:11:39They leave their cubs in the tidal areas while they hunt.
0:11:46 > 0:11:49This wolf is the pups' eldest brother.
0:11:49 > 0:11:53He's baby-sitting while the adults are away hunting.
0:11:53 > 0:11:55He doesn't have any food for the cubs,
0:11:55 > 0:11:57so they eat whatever they can find...
0:11:57 > 0:12:00even chewing the barnacles off the rocks.
0:12:09 > 0:12:14They, like the bears, are awaiting the arrival of the salmon.
0:12:23 > 0:12:26The adults return... and find an intruder.
0:12:28 > 0:12:31A hungry bear has wandered into their patch.
0:12:31 > 0:12:33GROWLING AND BARKING
0:12:35 > 0:12:40Coastal wolves will often kill and eat small bears.
0:12:49 > 0:12:51But this bear is very big.
0:13:06 > 0:13:08SNARLING AND WHINING
0:13:10 > 0:13:15Eventually, they decide that this one is just too big.
0:13:25 > 0:13:30By July, the bears are all getting very hungry indeed.
0:13:30 > 0:13:34And still the salmon are not here.
0:13:42 > 0:13:47And then, after two months of travelling across the open ocean,
0:13:47 > 0:13:48the salmon reach the coast.
0:13:54 > 0:13:59As they near the shore, they begin to smell fresh water.
0:14:06 > 0:14:10There are thousands of rivers flowing into the sea
0:14:10 > 0:14:13and the salmon have to find the particular one
0:14:13 > 0:14:15that will lead them to their birthplace.
0:14:18 > 0:14:22They have a truly extraordinary sense of smell.
0:14:25 > 0:14:29They can distinguish a single drop from their home river
0:14:29 > 0:14:32amongst eight million litres of sea water.
0:14:36 > 0:14:39As they detect the waters of home,
0:14:39 > 0:14:45they converge into the narrow fjords, which act as underwater corridors.
0:14:47 > 0:14:51But other creatures also know these corridors.
0:14:54 > 0:14:56Killer whales.
0:14:56 > 0:14:59They eat a lot of salmon.
0:15:06 > 0:15:09And so do Steller sea lions.
0:15:24 > 0:15:27Salmon sharks are here too...
0:15:27 > 0:15:30specifically to feed on salmon.
0:15:35 > 0:15:40But there is one predator that they can never see coming...
0:15:43 > 0:15:46..the bald-headed eagle.
0:16:32 > 0:16:35Once past these coastal predators,
0:16:35 > 0:16:39there is little to prevent them from reaching their home river.
0:16:39 > 0:16:40It's now late July,
0:16:40 > 0:16:45and the salmon are poised at the edge of their inland realm.
0:16:50 > 0:16:53In the estuaries of the larger rivers,
0:16:53 > 0:16:58all five species of Pacific salmon mingle together -
0:16:58 > 0:17:03Pink, Chum, Coho, Sockeye and Chinook.
0:17:09 > 0:17:12The drive to get into the rivers is strong.
0:17:12 > 0:17:15Their eggs will only survive in fresh water.
0:17:23 > 0:17:26In late July, however, the water level is often too low
0:17:26 > 0:17:30for the first salmon to enter the smaller rivers.
0:17:37 > 0:17:40That doesn't stop them trying.
0:17:43 > 0:17:48But the very water that has drawn them back home,
0:17:48 > 0:17:49will eventually kill them.
0:17:52 > 0:17:54As their kidneys and other organs
0:17:54 > 0:17:58adjust to the sudden lack of salt water,
0:17:58 > 0:18:00they stop eating and even drinking.
0:18:02 > 0:18:05So, the energy stored in their bodies
0:18:05 > 0:18:09is all they have to power their swim up river and spawn.
0:18:12 > 0:18:16However, the salmon in the smaller streams
0:18:16 > 0:18:19have a more immediate problem.
0:18:20 > 0:18:22The low water has stopped them
0:18:22 > 0:18:26before their journey upstream can even begin.
0:18:33 > 0:18:39But their coast, every year, is swept by great storms.
0:18:42 > 0:18:46In the skies above the north Pacific, a huge eddy is forming.
0:18:48 > 0:18:54It moves towards the coast and the high coastal mountains.
0:19:16 > 0:19:21The clouds are driven up and over this massive barrier,
0:19:21 > 0:19:24and they drop their load of water.
0:19:49 > 0:19:55The Great Forest gets up to three metres of rainfall a year.
0:20:02 > 0:20:05Bears have thick coats,
0:20:05 > 0:20:08and the heavy rain doesn't seem to bother them at all.
0:20:16 > 0:20:21The steep rocky mountains funnel the rainwater into the rivers
0:20:21 > 0:20:22and levels quickly rise.
0:20:34 > 0:20:38This is what the salmon have been waiting for.
0:20:47 > 0:20:51The first wave of travellers advance upstream.
0:20:57 > 0:21:02No sooner do they start, than they are faced with another challenge.
0:21:06 > 0:21:11But six million years of evolution have prepared the salmon well.
0:21:31 > 0:21:36Their bodies are solid muscle...
0:21:36 > 0:21:37and perfectly streamlined.
0:21:41 > 0:21:44Clearing these falls for a salmon
0:21:44 > 0:21:47is like a human being jumping over a four-story building.
0:22:00 > 0:22:05In many of these falls, however, the salmon face more than just water.
0:22:09 > 0:22:12The bears know that this is where they can get
0:22:12 > 0:22:14the first proper meal of the season.
0:22:18 > 0:22:19But it's not easy.
0:22:22 > 0:22:26There is an art to catching a leaping salmon...
0:22:29 > 0:22:33..and this young bear hasn't yet acquired it.
0:22:39 > 0:22:42This is what salmon were born to do.
0:22:50 > 0:22:54They are driven to get up these rivers to their spawning grounds.
0:22:55 > 0:22:57Their parents made it up here,
0:22:57 > 0:23:02and nothing short of death will stop them from repeating that journey.
0:23:06 > 0:23:11They are trying to get to the exact stretch of gravel where they hatched.
0:23:14 > 0:23:18Some lucky ones may only have to go a few miles inland.
0:23:18 > 0:23:22But others are faced with a truly daunting journey.
0:23:27 > 0:23:31The farthest that salmon have been known to swim up-river
0:23:31 > 0:23:33is 2,000 miles.
0:23:37 > 0:23:41Summer rains can be short, and when they stop,
0:23:41 > 0:23:45the water levels in many of the rivers along the coast drop quickly.
0:23:48 > 0:23:52The first salmon in the rivers are once again trapped by shallow water
0:23:52 > 0:23:55and worse - they're in bear country now.
0:23:59 > 0:24:00In early August,
0:24:00 > 0:24:03mother bears begin to patrol the rivers looking for fish.
0:24:03 > 0:24:07Like this one, they are usually skinny and starving.
0:24:16 > 0:24:19She and her cubs have eaten nothing but plants
0:24:19 > 0:24:22since they emerged from their den.
0:24:22 > 0:24:25They are in desperate need of a proper meal.
0:24:29 > 0:24:35Bears of all ages and experience come to the rivers to look for salmon.
0:24:39 > 0:24:43The first fish of the season, however, are hard to catch.
0:24:46 > 0:24:50This young bear is still learning how to do it.
0:24:50 > 0:24:53Step number one is spotting a salmon.
0:24:56 > 0:24:59A higher perspective usually helps.
0:25:02 > 0:25:07In these early days, fish are few and far between.
0:25:09 > 0:25:13And when they do appear, they are moving very fast.
0:25:42 > 0:25:46The salmon also have lots of places to hide.
0:25:46 > 0:25:49The rivers are only shallow in short stretches and they
0:25:49 > 0:25:53can quickly shoot across them and escape into the deep pools.
0:26:01 > 0:26:05This mother and her cubs are going to have to wait a little longer
0:26:05 > 0:26:07for the conditions to change
0:26:07 > 0:26:10before they can get the meals they so badly need.
0:26:16 > 0:26:22But for the salmon, these deep-water refuges are becoming prisons.
0:26:29 > 0:26:33It may be weeks before it rains again and they can move on.
0:26:38 > 0:26:42Their bodies are now beginning to change.
0:26:43 > 0:26:48As their sex hormones stimulate the production of eggs and sperm,
0:26:48 > 0:26:50their skin changes colour.
0:26:52 > 0:26:56Some develop a humped back and a hooked nose.
0:26:59 > 0:27:03All these changes use up precious energy.
0:27:03 > 0:27:07The longer the fish wait in these pools, the less likely they will be
0:27:07 > 0:27:10able to complete the journey to their spawning grounds.
0:27:15 > 0:27:18The mother bear and her cubs, finding little in the shallows,
0:27:18 > 0:27:22now try their luck in the deeper salmon-filled pools.
0:27:29 > 0:27:32The salmon are easy enough to see.
0:27:35 > 0:27:36With so many fish here,
0:27:36 > 0:27:40this young bear should surely be able to catch something.
0:27:46 > 0:27:49But finding the salmon is only part of the problem.
0:27:52 > 0:27:56Bears must pin a salmon to the stream bed in order to catch it.
0:27:56 > 0:27:58Not easy in deep water.
0:28:02 > 0:28:07Older bears know that it is almost impossible to get a meal this way.
0:28:10 > 0:28:14But while the salmon here may be relatively safe from the bears,
0:28:14 > 0:28:15they are not out of danger.
0:28:20 > 0:28:25The late summer sun is warming the water so that levels are dropping,
0:28:25 > 0:28:29and the amount of dissolved oxygen is decreasing.
0:28:33 > 0:28:38The time spent in these worsening conditions is beginning to show.
0:28:43 > 0:28:48The experienced bears show the youngsters what to do.
0:28:48 > 0:28:51Catching live salmon in these pools may be difficult.
0:28:51 > 0:28:54But there are dead ones for the taking,
0:28:54 > 0:28:57if only the bears can reach them.
0:29:02 > 0:29:07The problem is that most bears don't like to get their ears wet.
0:29:21 > 0:29:25However, the old bears know a trick or two.
0:29:33 > 0:29:36It just needs a little fancy footwork.
0:30:01 > 0:30:05This year, the water levels are particularly low,
0:30:05 > 0:30:09and by September, the salmon are in real trouble.
0:30:11 > 0:30:13In the confined, oxygen-poor water,
0:30:13 > 0:30:18there is an increased risk of parasites and infections.
0:30:21 > 0:30:25In some years, these conditions can get so bad
0:30:25 > 0:30:26that most of the salmon die
0:30:26 > 0:30:30before they even reach the spawning grounds.
0:30:35 > 0:30:38What they need is more rain
0:30:38 > 0:30:40and soon.
0:30:43 > 0:30:48Luckily, this year the autumn rains arrive on time.
0:31:14 > 0:31:17The salmon can set off once again.
0:31:19 > 0:31:24However, so much rain brings different challenges.
0:31:29 > 0:31:34The fish now have to battle against powerful torrents.
0:31:45 > 0:31:50But the salmon know how to turn this swift turbulent water
0:31:50 > 0:31:52to their own advantage.
0:32:05 > 0:32:10Scarcely beating their tails, they manage to propel themselves forward
0:32:10 > 0:32:12by using the energy of the water,
0:32:12 > 0:32:16much as a sailboat does when tacking into the wind.
0:32:42 > 0:32:45But that doesn't mean there will be no further problem
0:32:45 > 0:32:47in reaching the spawning grounds.
0:33:08 > 0:33:13This is going to be the end of the road for a lot of salmon.
0:33:15 > 0:33:17These bears are really hungry.
0:33:17 > 0:33:20They haven't tasted salmon for 10 months
0:33:20 > 0:33:24and the big males battle for the best fishing spots.
0:33:29 > 0:33:33The longer the salmon take over their journey upstream,
0:33:33 > 0:33:35the weaker they become.
0:33:38 > 0:33:43And these falls present them with their biggest challenge yet.
0:33:44 > 0:33:48Although the falls aren't very tall, the bears hold the high ground.
0:33:50 > 0:33:56The salmon make short exploratory leaps to see where the bears are.
0:34:10 > 0:34:13But they don't always get it right.
0:34:19 > 0:34:23This mother bear has been waiting months for this moment.
0:34:25 > 0:34:28Competition is fierce for these first salmon -
0:34:28 > 0:34:31even between a mother and her own cubs.
0:34:36 > 0:34:40More and more fish arrive at the foot of the falls.
0:34:50 > 0:34:55Eventually, they have to go for it, regardless of the danger.
0:35:33 > 0:35:36But numbers are on their side.
0:35:36 > 0:35:42For every salmon that gets caught, hundreds make it past the bears.
0:36:14 > 0:36:15By early September,
0:36:15 > 0:36:19the salmon have almost reached their spawning grounds -
0:36:19 > 0:36:25that one particular patch of gravel where they hatched, four years ago.
0:36:29 > 0:36:32The salmon have now travelled far inland
0:36:32 > 0:36:36and can be found from California to the Arctic Ocean,
0:36:36 > 0:36:40across a fifth of the entire continent of North America.
0:36:57 > 0:37:00But the journey has taken a heavy toll.
0:37:02 > 0:37:07For every thousand that hatched, only four manage to return.
0:37:11 > 0:37:14And even for those salmon that have made it back,
0:37:14 > 0:37:16there are still more dangers.
0:37:16 > 0:37:18They have finally reached the end of their road,
0:37:18 > 0:37:22and are so tired and battered that they are easy prey.
0:37:22 > 0:37:26The advantage is fully to the bears now.
0:38:34 > 0:38:37The bears are spoiled for choice.
0:38:41 > 0:38:43In the best spawning areas,
0:38:43 > 0:38:46there are thousands of salmon in every mile of river.
0:38:51 > 0:38:54The bears here will gorge themselves for the next two months,
0:38:54 > 0:38:56and the mothers with their cubs can now gain
0:38:56 > 0:39:00the weight they will need if they are to make it through the coming winter.
0:39:13 > 0:39:18The salmon are so abundant that even the little cub is having a go.
0:39:27 > 0:39:32He has caught a female pink, the smallest of the salmon species.
0:39:35 > 0:39:39He is already learning the skills he will need to survive as an adult.
0:39:45 > 0:39:47But he's got a little way to go yet.
0:39:52 > 0:39:55Although the salmon are now at the mercy of the bears,
0:39:55 > 0:39:57they will not leave this place.
0:39:57 > 0:40:02Their nature impels them to lay their eggs where they themselves were born.
0:40:11 > 0:40:13Even though the bears eat their fill,
0:40:13 > 0:40:17there are so many salmon that most will survive to spawn.
0:40:23 > 0:40:28The sockeye salmon's brilliant colour signals that they are ready to breed.
0:40:29 > 0:40:34Males battle with each other for position behind the females.
0:40:42 > 0:40:46The female digs out a shallow scoop as a nest.
0:40:57 > 0:40:59The male nestles up against the female,
0:40:59 > 0:41:02stimulating her to release her eggs.
0:41:05 > 0:41:08When she is ready, she lowers herself over the nest.
0:41:08 > 0:41:10She begins to turn out her eggs
0:41:10 > 0:41:14and the male releases a cloud of sperm into the water.
0:41:32 > 0:41:36These salmon are the lottery winners -
0:41:36 > 0:41:40the lucky ones that have succeeded in returning here to spawn.
0:41:41 > 0:41:45But there are enough of them to seed the next generation.
0:41:52 > 0:41:55The spawning season is a time of extreme abundance,
0:41:55 > 0:41:59for in the course of ensuring their own survival,
0:41:59 > 0:42:03the salmon provide food for a horde of other creatures.
0:42:09 > 0:42:12These Bonaparte gulls
0:42:12 > 0:42:17are collecting one of the season's great delicacies...salmon eggs.
0:42:37 > 0:42:42For the bears, the salmon spawning season is the pinnacle of the year.
0:42:48 > 0:42:54But for the salmon, it is the pinnacle of their entire lives.
0:42:59 > 0:43:02All that have reached it
0:43:02 > 0:43:06will end their days in the very place where they began them.
0:43:15 > 0:43:20The wear and tear of their long journey is now showing.
0:43:25 > 0:43:29Their bodies have been deteriorating for weeks,
0:43:29 > 0:43:34and with this last act of reproduction, they are finally spent.
0:43:55 > 0:43:57But, even in death,
0:43:57 > 0:44:01the salmon continue to benefit the animals of the forest.
0:44:06 > 0:44:12The mother and her cubs will continue to fatten themselves on the carcasses
0:44:12 > 0:44:16until they are ready to head back up the mountain, to den in November.
0:44:21 > 0:44:25Why Pacific salmon have to die after they reproduce
0:44:25 > 0:44:28is not clearly understood.
0:44:28 > 0:44:30Atlantic salmon don't,
0:44:30 > 0:44:33they return year after year to spawn.
0:44:33 > 0:44:37But the Pacific salmons' decaying bodies nourish the rivers,
0:44:37 > 0:44:40providing abundant food for their growing eggs.
0:44:42 > 0:44:47And that is what it has all been about for the salmon.
0:44:47 > 0:44:52All their trials and tribulations have ensured that the baby salmon,
0:44:52 > 0:44:55when they emerge from these beautiful orange globes,
0:44:55 > 0:44:57will have everything they need
0:44:57 > 0:45:01to begin this incredible journey all over again.
0:45:10 > 0:45:15But the legacy of the salmon extends far beyond the rivers and streams.
0:45:18 > 0:45:22They are at the heart of a massive network of life.
0:45:24 > 0:45:28There are more than 200 species in the Great Forest alone -
0:45:28 > 0:45:31plants and insects, birds and mammals -
0:45:31 > 0:45:33that depend on the salmon.
0:45:39 > 0:45:40It's possible that Pacific salmon,
0:45:40 > 0:45:44between their time out at sea and their time inland,
0:45:44 > 0:45:49feed more life than any other animal species on the planet.
0:45:53 > 0:45:58And there is one more beneficiary of the salmon's legacy...
0:46:03 > 0:46:08..the fish are a unique link between the ocean and the forest.
0:46:14 > 0:46:18Born in fresh water, they live their life in the sea
0:46:18 > 0:46:22and there gather nutrients with which they build their bodies.
0:46:28 > 0:46:32Now, scattered by feeding bears and wolves,
0:46:32 > 0:46:37the last bequest of these salmon is to the forest.
0:46:46 > 0:46:51Nitrogen, carbon and phosphorus that was gathered in the ocean
0:46:51 > 0:46:54is now released from their decaying bodies...
0:46:59 > 0:47:04..providing the nutrients that enable these trees -
0:47:04 > 0:47:05Sitka spruce...
0:47:07 > 0:47:08..red cedar...
0:47:10 > 0:47:11..and western hemlock...
0:47:13 > 0:47:16..to grow to such prodigious heights.
0:47:19 > 0:47:24It is now known that 80% of the nitrogen in these coastal forests
0:47:24 > 0:47:28where the salmon spawn, comes from the sea,
0:47:28 > 0:47:31carried in the bodies of the returning fish.
0:47:36 > 0:47:40The trees may be growing hundreds of miles from the ocean,
0:47:40 > 0:47:43but they are still nourished by its richness.
0:47:47 > 0:47:49The rivers of the Great Forest,
0:47:49 > 0:47:54like the veins and arteries of an animal, carry its life blood,
0:47:54 > 0:47:57the Pacific salmon, throughout.
0:48:04 > 0:48:09And no animal relies on them more than the grizzly bear.
0:48:14 > 0:48:18Thanks in large part to the abundance of the salmon run,
0:48:18 > 0:48:23these cubs have survived their first and most difficult year.
0:48:24 > 0:48:27The bears will sleep easy each winter
0:48:27 > 0:48:33as long as the Pacific Salmon are able to continue their epic run -
0:48:33 > 0:48:36one of Nature's Great Events.
0:49:02 > 0:49:07In making The Great Salmon Run, film-maker Jeff Turner wanted
0:49:07 > 0:49:11to discover exactly how grizzly bears caught salmon underwater.
0:49:21 > 0:49:23But his quest was to take him deeper
0:49:23 > 0:49:27into the world of the grizzly than he had ever imagined.
0:49:35 > 0:49:38The first challenge that Jeff and the team faced
0:49:38 > 0:49:41was to get their latest high-definition camera systems
0:49:41 > 0:49:43into the wilds of British Columbia.
0:49:43 > 0:49:45This is modern day wildlife film-making -
0:49:45 > 0:49:49we can't go anywhere without about half a ton of gear.
0:49:49 > 0:49:52It's very discreet. Animals don't notice us at all(!)
0:49:53 > 0:49:57Jeff has more than 20 years' experience of filming grizzlies,
0:49:57 > 0:50:01and knows how to work with them in the wild better than anyone.
0:50:02 > 0:50:04I was just talking to Justin.
0:50:04 > 0:50:10He was telling me he just came back from a shoot in Indonesia.
0:50:10 > 0:50:12He said he had 15 porters.
0:50:12 > 0:50:16I think... I think we must be doing something wrong!
0:50:16 > 0:50:21Jeff knows that the only way to film wild grizzlies
0:50:21 > 0:50:22is with a small crew...
0:50:22 > 0:50:24and a very sensitive approach.
0:50:26 > 0:50:28In order to get the shots he wanted,
0:50:28 > 0:50:33he used a new digital camera in a specially-built underwater housing
0:50:33 > 0:50:36that he could set up close to the fishing bears,
0:50:36 > 0:50:37without disturbing them.
0:50:37 > 0:50:41Getting the camera in place can be tricky, however.
0:50:41 > 0:50:44Experience has taught him how to put them at ease
0:50:44 > 0:50:46with just the right tone of voice.
0:50:46 > 0:50:48Hey, bear, how ya doin', hey?
0:50:48 > 0:50:51I'm going to scare some fish up there for ya.
0:50:51 > 0:50:53That's a good bear.
0:50:53 > 0:50:55I won't bother you. I won't be long.
0:51:01 > 0:51:03This is when you need six hands.
0:51:03 > 0:51:08The wild bears seemed intrigued by this visitor to their river.
0:51:08 > 0:51:10You guys are as excited about this as I am.
0:51:12 > 0:51:17What Jeff was hoping to capture was a shot of bears catching salmon
0:51:17 > 0:51:20from both above and below water.
0:51:20 > 0:51:24He needed to operate the camera from a distance
0:51:24 > 0:51:27so that the bears would be so relaxed they would continue fishing.
0:51:29 > 0:51:32But that meant connecting the camera to his computer,
0:51:32 > 0:51:34using fibre-optic cable.
0:51:34 > 0:51:36If they come through here they may catch on it...
0:51:36 > 0:51:41And all that cable in the river proved too much of a temptation
0:51:41 > 0:51:44for one particularly mischievous young bear...
0:51:44 > 0:51:48a situation that called for some firm bear-talk from Jeff.
0:51:48 > 0:51:52Hey, hey, hey, hey, hey. Drop that.
0:51:52 > 0:51:53Yah, yah, yah!
0:51:59 > 0:52:02You guys can't bite the cable.
0:52:02 > 0:52:06Jeez! Ah...
0:52:06 > 0:52:09Luckily, the camera was still working.
0:52:10 > 0:52:13But Jeff soon realised that the salmon were avoiding
0:52:13 > 0:52:16the shallow waters and he wasn't getting the shots he wanted.
0:52:18 > 0:52:20The bears were being drawn to the deep pools
0:52:20 > 0:52:23where the salmon were hiding out.
0:52:24 > 0:52:26He had to try a new approach.
0:52:28 > 0:52:31The water levels in the creek are low and dropping
0:52:31 > 0:52:34and it means that the salmon that are in the system now
0:52:34 > 0:52:38are not moving and are staying in the deeper pools.
0:52:38 > 0:52:41So it means that if the fish won't come to me,
0:52:41 > 0:52:44I'm going to have to go to the fish.
0:52:46 > 0:52:51Since he didn't have a shaggy fur coat, Jeff squeezed into a dry suit
0:52:51 > 0:52:53to protect himself against the icy water.
0:52:55 > 0:52:59The camera needed to be on the bottom of the pool, some three-metres deep.
0:52:59 > 0:53:02But getting down there in an air-filled dry suit
0:53:02 > 0:53:04was no easy matter.
0:53:13 > 0:53:15I'm bobbing.
0:53:15 > 0:53:18Jeff clearly needed to put on some weight.
0:53:21 > 0:53:24I feel like I'm in some medieval movie or something.
0:53:26 > 0:53:28Mel Brookes or something!
0:53:30 > 0:53:32Young Frankenstein. OK.
0:53:39 > 0:53:42With his improvised diving belt,
0:53:42 > 0:53:46he could now get down deep enough to position the camera.
0:53:51 > 0:53:55The bears were learning very quickly that Jeff and his crew
0:53:55 > 0:53:56were not a threat.
0:53:56 > 0:54:01They watched him curiously as he retreated to a respectful distance
0:54:01 > 0:54:03and controlled his camera from his laptop.
0:54:06 > 0:54:09What would the bears do next?
0:54:15 > 0:54:19He didn't have to wait long before the first bear waded into the pool.
0:54:20 > 0:54:23But this youngster seemed totally out of his depth.
0:54:23 > 0:54:26This is really funny. This little guy -
0:54:26 > 0:54:30he doesn't know how to get down, so he can't quite reach the bottom.
0:54:32 > 0:54:33So he is just hanging,
0:54:33 > 0:54:36bobbing along here.
0:54:43 > 0:54:44He's got his paw on it!
0:54:45 > 0:54:47Damn it, he knocked it over.
0:54:49 > 0:54:54I think he used it to stand on to kick himself off.
0:54:55 > 0:54:59The fish we've got are going straight downhill!
0:54:59 > 0:55:01It's a really steep river(!)
0:55:01 > 0:55:06It was back into the chilly water for Jeff to realign his camera.
0:55:17 > 0:55:22Soon it was up and running again and getting some intimate shots.
0:55:22 > 0:55:25Got a good shot of his privates.
0:55:30 > 0:55:32Although the salmon were still just out of reach
0:55:32 > 0:55:36of this persistent young bear, the camera wasn't.
0:55:36 > 0:55:38Oh, no, he's getting close to the camera.
0:55:38 > 0:55:42Be careful, bear. Ah, shoot!
0:55:44 > 0:55:47He totally knocked it over.
0:55:47 > 0:55:50I'm going to have to reposition that camera again.
0:55:51 > 0:55:54The youngster continued to cause problems.
0:55:54 > 0:55:56He kept on knocking over the camera.
0:56:03 > 0:56:07Then, two bigger, more experienced bears appeared on the scene,
0:56:07 > 0:56:09right in front of Jeff.
0:56:15 > 0:56:19But the remote camera was having trouble keeping up with the action.
0:56:24 > 0:56:29To discover exactly what was going on, Jeff needed a new perspective.
0:56:29 > 0:56:32These bears were so unfazed by his presence
0:56:32 > 0:56:34that he decided to stay in the water
0:56:34 > 0:56:38and hand-hold the camera on the end of a long pole.
0:56:46 > 0:56:49The bears were learning to trust Jeff,
0:56:49 > 0:56:51allowing him to get even closer.
0:56:54 > 0:56:58To get as intimate as this with wild grizzlies
0:56:58 > 0:57:00is potentially extremely dangerous
0:57:00 > 0:57:04and required all of Jeff's many years of experience.
0:57:04 > 0:57:05That was good.
0:57:08 > 0:57:10OK, we've got this other guy coming out too now.
0:57:17 > 0:57:20He's going to check it out. It's OK, you can have a look at it.
0:57:20 > 0:57:23He was now close enough to observe their technique in detail.
0:57:23 > 0:57:26This was something that Jeff had never seen before.
0:57:26 > 0:57:29By kicking the salmon into the shallows,
0:57:29 > 0:57:34the more experienced bears were able to grab themselves an easy meal.
0:57:34 > 0:57:38And by hand-holding the camera, Jeff could follow the action.
0:57:44 > 0:57:46OK, we're getting close here.
0:57:47 > 0:57:50He's coming up to you right now...roll.
0:57:50 > 0:57:56To get as close as this to an adult grizzly bear is truly remarkable.
0:57:56 > 0:57:58Jeff makes it look easy,
0:57:58 > 0:58:02but it takes years of experience and understanding.
0:58:06 > 0:58:09OK, good show, guys. Thank you. That's it.
0:58:09 > 0:58:13We're done. Yep, time to go. That's it.
0:58:15 > 0:58:18Jeff had managed to enter the bear's world,
0:58:18 > 0:58:20giving him the most intimate shots
0:58:20 > 0:58:23of grizzlies fishing underwater ever filmed.
0:58:23 > 0:58:27He had achieved this not just by using new technology,
0:58:27 > 0:58:30but through his own special understanding
0:58:30 > 0:58:32of these incredible animals.
0:58:58 > 0:59:01Subtitles by Red Bee Media Ltd
0:59:01 > 0:59:04E-mail subtitling@bbc.co.uk