0:00:02 > 0:00:04They call it America's last frontier.
0:00:08 > 0:00:10500,000 square miles of wilderness.
0:00:12 > 0:00:14This is Alaska.
0:00:17 > 0:00:20Home to some of the hardiest animals on the planet.
0:00:27 > 0:00:29Alaskan seasons run fast and furious.
0:00:39 > 0:00:41Opportunities are fleeting.
0:00:43 > 0:00:46For people as well as animals.
0:00:47 > 0:00:50Survival means making the most of nature's gold rush.
0:00:52 > 0:00:54Play it right, and you will hit the jackpot.
0:00:56 > 0:01:00Get it wrong, and you could lose it all.
0:01:03 > 0:01:07It's not about your size, it's about your attitude.
0:01:08 > 0:01:10This land belongs to the bold.
0:01:13 > 0:01:15This is Alaska.
0:01:27 > 0:01:32It's March and Alaska's far north is frozen solid.
0:01:33 > 0:01:36For 65 days, this place was in permanent darkness.
0:01:40 > 0:01:43But things round here are about to change.
0:01:49 > 0:01:53Polar bears have spent the winter hunting across thousands
0:01:53 > 0:01:54of miles of sea ice.
0:01:56 > 0:01:58But the ice is beginning to melt.
0:02:02 > 0:02:06In a few short months, 24-hour darkness
0:02:06 > 0:02:09will become 24-hour daylight.
0:02:12 > 0:02:15The great seasonal transformation has begun.
0:02:22 > 0:02:25The polar bears will have to scratch a living on land.
0:02:26 > 0:02:30But for everyone else, the good times are just around the corner.
0:02:48 > 0:02:53Of all the states in America, Alaska is by far the biggest
0:02:53 > 0:02:54and the most northerly.
0:02:56 > 0:02:59A third of it lies above the Arctic Circle.
0:03:01 > 0:03:03Temperatures can drop to 80 below.
0:03:05 > 0:03:07The pale rays of early spring
0:03:07 > 0:03:09hardly seem up to the task of warming anything.
0:03:13 > 0:03:17Across Alaska, thousands of rivers lie frozen.
0:03:17 > 0:03:20There are three million iced-up lakes.
0:03:20 > 0:03:2225,000 glaciers.
0:03:24 > 0:03:26Even the waterfalls have stopped mid-fall.
0:03:35 > 0:03:36Nothing moves.
0:03:43 > 0:03:47When the sun does finally unlock the land,
0:03:47 > 0:03:49every opportunist will be waiting.
0:03:52 > 0:03:54The North Slope -
0:03:54 > 0:03:56the coldest, wildest part of all Alaska.
0:03:59 > 0:04:01This is the tundra.
0:04:03 > 0:04:06Even trees struggle to take root in the icy soil.
0:04:09 > 0:04:10But life is possible even here.
0:04:14 > 0:04:16An arctic ground squirrel.
0:04:17 > 0:04:20He spends his entire winter asleep.
0:04:20 > 0:04:23Out like a light for eight months straight -
0:04:23 > 0:04:27the longest, deepest hibernation of any animal on earth.
0:04:29 > 0:04:32This is one extreme lifestyle can only be seen
0:04:32 > 0:04:34using a special filming burrow.
0:04:38 > 0:04:40He's pretty much stopped breathing.
0:04:40 > 0:04:42His heart is barely beating.
0:04:48 > 0:04:50The sun is getting higher every day.
0:04:56 > 0:05:00In the darkness of his burrow, the squirrel's body clock
0:05:00 > 0:05:01drags him out of bed.
0:05:02 > 0:05:04There's no time to waste.
0:05:24 > 0:05:27Last time he saw it, back in the autumn,
0:05:27 > 0:05:29this was his territory.
0:05:29 > 0:05:31Now he's got to fight for it all over again.
0:05:37 > 0:05:40For the next two weeks, he'll barely have time even to eat.
0:05:46 > 0:05:49It's a constant battle to keep rival males of his turf.
0:06:14 > 0:06:17There's a sense of anticipation in the air.
0:06:21 > 0:06:24Females emerge a few days later.
0:06:26 > 0:06:28He won't want to miss his first date.
0:06:30 > 0:06:32And there she is.
0:06:42 > 0:06:43But what is he doing?
0:06:49 > 0:06:51SQUIRREL CHIRPS
0:06:52 > 0:06:57She'll only be fertile for 12 hours in the entire year.
0:06:59 > 0:07:02- SQUIRREL CHIRPS - There's no time for hesitation.
0:07:11 > 0:07:13He cautiously makes his move.
0:07:17 > 0:07:21She might be in a hurry, but she can still be choosy.
0:07:35 > 0:07:38He knows that while there are other males around,
0:07:38 > 0:07:40she could easily go off with someone else.
0:07:43 > 0:07:45He won't leave her side for 24 hours.
0:07:54 > 0:07:56An Alaskan spring moves fast
0:07:56 > 0:07:58and if you don't seize the moment,
0:07:58 > 0:07:59it will pass you by.
0:08:05 > 0:08:07The exact arrival of spring is hard to predict.
0:08:14 > 0:08:17But for some, working out when it might arrive
0:08:17 > 0:08:19has become a total obsession.
0:08:21 > 0:08:23CHAIN SAW ROARS
0:08:27 > 0:08:29Deep in central Alaska,
0:08:29 > 0:08:32the Tanana River freezes to over one metre down.
0:08:34 > 0:08:37And every Spring the townsfolk look forward to the day
0:08:37 > 0:08:39when it will break up and flow again.
0:08:42 > 0:08:44It's such a big deal
0:08:44 > 0:08:47they've held a festival for nearly 100 years to celebrate.
0:08:50 > 0:08:54It begins on 1st March with the digging out
0:08:54 > 0:08:56of the heart of the frozen river...
0:08:58 > 0:09:00..setting the stage for a truly Alaskan event.
0:09:08 > 0:09:10The whole town joins in.
0:09:15 > 0:09:16On the count of three.
0:09:16 > 0:09:19One...
0:09:19 > 0:09:21Two...
0:09:21 > 0:09:22Three.
0:09:31 > 0:09:35The day the river breaks up, this wooden tripod will fall,
0:09:35 > 0:09:39marking the first day of spring - a day everyone is waiting for.
0:09:43 > 0:09:47OK, that's it. We're done. Good job, everyone. Thank you.
0:09:47 > 0:09:49THEY CHEER
0:09:55 > 0:09:57As part of the celebrations,
0:09:57 > 0:10:01everyone has a bet or two on when the tripod will actually drop.
0:10:02 > 0:10:05Whoever gets it right, to the nearest second,
0:10:05 > 0:10:06will hit the jackpot.
0:10:12 > 0:10:14And then the wait...
0:10:14 > 0:10:16begins.
0:10:18 > 0:10:21The tripod is tethered to a watchtower
0:10:21 > 0:10:25where the official clock will stop as soon as the tripod collapses.
0:10:27 > 0:10:31They take it so seriously, there is even a watchman on 24-hour duty.
0:10:41 > 0:10:43The nights become shorter.
0:10:43 > 0:10:45Still, the tripod stands.
0:10:54 > 0:10:57Each day bulks up with seven minutes more daylight.
0:11:10 > 0:11:13Four weeks later, the tripod is starting to shift.
0:11:22 > 0:11:26At long last, on 25th April,
0:11:26 > 0:11:28at 3.48 in the afternoon,
0:11:28 > 0:11:30spring arrives.
0:11:32 > 0:11:35SIREN BLARES
0:11:40 > 0:11:44Round here, though, they don't call it spring.
0:11:44 > 0:11:47This season is what they call 'break-up.'
0:11:47 > 0:11:50The thawing of the rivers is a season all of its own.
0:11:51 > 0:11:54That's how much it means to an Alaskan soul.
0:12:02 > 0:12:05The sun's power has started to revive Alaska's heart.
0:12:17 > 0:12:21365,000 miles of rivers will break up within a matter of weeks.
0:12:34 > 0:12:36Life is getting going again.
0:12:36 > 0:12:40Stoneflies have been waiting under the ice all winter.
0:12:40 > 0:12:43With the melt, they are released into the daylight.
0:12:57 > 0:13:00American dippers follow the rivers as they thaw.
0:13:01 > 0:13:05For everyone that's braved the cold, it's payback time.
0:13:05 > 0:13:07BIRD CHIRPS
0:13:11 > 0:13:16A porcupine has spent the winter up trees, eating nothing but bark.
0:13:16 > 0:13:20Now he's off to look for the first tender shoots of spring.
0:13:24 > 0:13:27This willow ptarmigan has been sleeping in snowdrifts
0:13:27 > 0:13:29to fend off the cold.
0:13:29 > 0:13:32But he's starting to shed his white winter feathers,
0:13:32 > 0:13:34looking forward to better times.
0:13:42 > 0:13:45It's still too cold for most plants to get going.
0:13:49 > 0:13:52In the Chugach Mountain Range though,
0:13:52 > 0:13:54there's one that's staked an early claim.
0:14:04 > 0:14:06It's a woolly lousewort.
0:14:09 > 0:14:13The fur wrapping acts like a greenhouse.
0:14:13 > 0:14:17Even on frosty mornings, the woolly lousewort is several degrees
0:14:17 > 0:14:19warmer than the air around it.
0:14:31 > 0:14:35This bold little pioneer now has enough of a head start
0:14:35 > 0:14:38to produce the some of the first flowers of an Alaskan spring.
0:14:50 > 0:14:53And it's ready with nectar for an early bee.
0:15:03 > 0:15:06All across Alaska, spring's roll call has started.
0:15:16 > 0:15:20As the sun penetrates even the deepest woods,
0:15:20 > 0:15:24100,000 black bears will emerge from hibernation.
0:15:28 > 0:15:31Most will have made their winter dens on the ground,
0:15:31 > 0:15:33but this bear made hers higher up.
0:15:37 > 0:15:42She's spent the last seven months in a hole inside a cottonwood tree,
0:15:42 > 0:15:44five metres above the forest floor.
0:15:51 > 0:15:55She's out, and she's not on her own.
0:16:01 > 0:16:05Perched several metres above her are her two small cubs,
0:16:05 > 0:16:09born inside the tree, and venturing out for the first time.
0:16:17 > 0:16:20Their tree den was the safest start for them,
0:16:20 > 0:16:22away from attack by other bears.
0:16:26 > 0:16:29Somehow, she's going to have to get them down.
0:16:38 > 0:16:40They're only around 12 weeks old,
0:16:40 > 0:16:45and they already have strong claws and a natural instinct to climb.
0:16:49 > 0:16:51But when you're this new to tree-climbing,
0:16:51 > 0:16:53it's a little bit daunting.
0:17:03 > 0:17:05The first cub seems to be a natural.
0:17:29 > 0:17:31But his brother is still way up the tree.
0:17:36 > 0:17:39BEAR CUB WHINES
0:17:54 > 0:17:56He's still not sure what to do next.
0:18:07 > 0:18:11A fall from this height would probably kill him.
0:18:11 > 0:18:14BEAR CUB WHINES
0:18:33 > 0:18:36BEAR CUB WHINES
0:18:49 > 0:18:53A little gentle encouragement is all he really needs.
0:18:57 > 0:19:00For an animal weighing 100kg,
0:19:00 > 0:19:02balancing on a branch looks precarious.
0:19:05 > 0:19:07But for black bears, climbing is a way of life.
0:19:14 > 0:19:17Trees will be their refuge for their entire lives.
0:19:37 > 0:19:40Their mother's devotion is total.
0:19:40 > 0:19:43She won't leave their side for another year or more.
0:19:56 > 0:19:58They have energy to burn
0:19:58 > 0:20:01and they'll spend hours a day play-fighting.
0:20:09 > 0:20:14But mum has lost a third of her body weight over the winter.
0:20:14 > 0:20:16She has to keep eating for all three of them.
0:20:16 > 0:20:18And there's not much around.
0:20:24 > 0:20:28This is what Alaskan old-timers call the starving time.
0:20:38 > 0:20:44This close to the Arctic Circle, winter is never far away.
0:20:44 > 0:20:46All it needs is a change in the wind direction.
0:20:54 > 0:20:58Raging winds from the North Pacific scream across the ocean,
0:20:58 > 0:21:01picking up moisture, creating a blizzard.
0:21:34 > 0:21:37WINDS GUST
0:21:45 > 0:21:48For these sea otters, life couldn't get much worse.
0:21:52 > 0:21:53It's 20 below.
0:21:59 > 0:22:02Mothers are trying to protect their newborn babies
0:22:02 > 0:22:03in the teeth of a sudden freeze.
0:22:10 > 0:22:13This tiny pup was only a few days old.
0:22:15 > 0:22:18Spring can be deadly when your luck runs out.
0:22:26 > 0:22:30Some sea otters find ways to avoid the worst of the storms.
0:22:32 > 0:22:37This is Valdez, the snowiest coastal town in Alaska.
0:22:40 > 0:22:43Like many harbours, it's abandoned for the winter.
0:22:45 > 0:22:47No-one likes to fish in these conditions.
0:22:49 > 0:22:51Well, almost no-one.
0:22:52 > 0:22:56In the calm waters, a lone male otter fishes for mussels.
0:22:58 > 0:23:00He eats a quarter of his body weight every day.
0:23:03 > 0:23:05It's snowing a little, but he's OK.
0:23:06 > 0:23:08He has the densest fur of any animal.
0:23:16 > 0:23:21Nearby, another sea otter has discovered her own little sanctuary.
0:23:21 > 0:23:24She has a baby just days old,
0:23:24 > 0:23:26- OTTER SQUEAKS - and he's taking all her attention.
0:23:39 > 0:23:42She needs to keep him warm and dry,
0:23:42 > 0:23:44so she preens him for hours at a time.
0:23:49 > 0:23:54She even blows air into his fur - the fluffier she can make it,
0:23:54 > 0:23:56the warmer he will be.
0:23:59 > 0:24:02With a baby to nurse, she needs to eat twice as much as normal.
0:24:06 > 0:24:09Sooner or later, she will have to leave him in the water
0:24:09 > 0:24:11while she finds food for herself.
0:24:11 > 0:24:14The problem is - he can't swim yet.
0:24:16 > 0:24:19MACHINE RUMBLES
0:24:22 > 0:24:25Everyone is impatient,
0:24:25 > 0:24:27trying to get rid of the snow.
0:24:33 > 0:24:36Just as it seems it will never get warm again...
0:24:38 > 0:24:42..the sun returns, the sea calms, and the fishermen get their boats
0:24:42 > 0:24:45ready for the start of the Alaskan fishing season.
0:24:45 > 0:24:47Smells like money, eh, boys?
0:24:49 > 0:24:52HORN WHISTLES
0:24:59 > 0:25:03As the harbour gets busier, the otters move on.
0:25:03 > 0:25:05But the days of shelter have been life-savers.
0:25:15 > 0:25:19Mum takes her growing pup out into the open water,
0:25:19 > 0:25:21and she has a surprise for him.
0:25:31 > 0:25:34Suddenly, he's all on his own.
0:25:34 > 0:25:36- But he can't go anywhere. - OTTER WHINES
0:25:36 > 0:25:39His mother has fluffed him up so much he's unsinkable.
0:25:42 > 0:25:46OTTER WHINES
0:25:46 > 0:25:48He can't do much but go round in circles.
0:25:59 > 0:26:04Once she's fed herself, she can scoop him back up and feed him too.
0:26:13 > 0:26:16She'll be looking after him like this for the next six months.
0:26:22 > 0:26:26The cold seas off southern Alaska are some of the richest on earth.
0:26:39 > 0:26:42The longline fishing season has just opened,
0:26:42 > 0:26:44and the crew of the Magia are out early.
0:26:46 > 0:26:49Round here, the prizes are big...
0:26:50 > 0:26:51..but so is the competition.
0:26:57 > 0:27:02These fishermen could make 60,000 in just a few days.
0:27:03 > 0:27:07They need to be ready. If they get it wrong, they lose everything.
0:27:12 > 0:27:16The biggest prizes are in the deepest water.
0:27:16 > 0:27:19But not many fishermen have the gear to work here.
0:27:19 > 0:27:22You need five miles of lines and hooks
0:27:22 > 0:27:26and the latest technology to even stand a chance.
0:27:31 > 0:27:35They're after black cod, one of the most prized fish in Alaska.
0:27:49 > 0:27:52Hundreds of dollars worth of bait gets cut to size
0:27:52 > 0:27:53and loaded onto the hooks.
0:27:59 > 0:28:02Then the lines are sent half a mile to the bottom of the ocean.
0:28:12 > 0:28:14This is longlining.
0:28:16 > 0:28:17And the waiting begins.
0:28:44 > 0:28:46By dawn, the scene has been set
0:28:46 > 0:28:49for one of nature's most audacious heists.
0:29:08 > 0:29:10The boat is surrounded.
0:29:16 > 0:29:20Sperm whales, 50 tonnes apiece.
0:29:27 > 0:29:29There are six of them, maybe more.
0:29:34 > 0:29:36For the crew, this spells disaster.
0:29:38 > 0:29:41- With this many whales, it's pretty much game over.- Yeah.
0:29:45 > 0:29:48'You see a spout and you know we are in trouble.
0:29:50 > 0:29:53'They're prowling, waiting to come upon us.
0:29:55 > 0:29:56'They're premeditated.'
0:30:00 > 0:30:03These whales are nearly 20 metres long.
0:30:03 > 0:30:05They're as big as the boat.
0:30:07 > 0:30:08And they're smart.
0:30:09 > 0:30:12They can recognise an individual fishing boat
0:30:12 > 0:30:14just by the noise of its engine.
0:30:21 > 0:30:24The lines are now full of fish, it's time to haul in the catch.
0:30:25 > 0:30:28The captain kicks the engine into gear.
0:30:29 > 0:30:31But he just can't pull them in quick enough.
0:30:31 > 0:30:33ENGINE RUMBLES
0:30:33 > 0:30:35This noise is like a dinner bell for whales.
0:30:37 > 0:30:39Down she goes!
0:30:41 > 0:30:43One by one, they dive.
0:30:50 > 0:30:52And the crew can do nothing about it.
0:30:58 > 0:31:02The whales carefully follow the lines down into the darkness.
0:31:05 > 0:31:07They zone in with their sonar.
0:31:11 > 0:31:13Then, with their long jaws,
0:31:13 > 0:31:17they delicately work the fish off the line.
0:31:17 > 0:31:21It's the perfect sting and the easiest meal in the sea.
0:31:32 > 0:31:35The crew haul their lines to the surface,
0:31:35 > 0:31:37but it's pretty much a waste of time.
0:31:40 > 0:31:42All that's left are some red rockfish
0:31:42 > 0:31:43that the whales didn't want...
0:31:47 > 0:31:51..a few bent hooks...
0:31:51 > 0:31:55and the chewed remains of the precious black cod.
0:31:55 > 0:31:57That's all the whales leave us!
0:31:59 > 0:32:02The crew think they've lost 90% of today's catch to the whales.
0:32:11 > 0:32:12No market for those.
0:32:14 > 0:32:17The four-day fishing trip should have paid up well.
0:32:17 > 0:32:19But now they'll go home empty handed.
0:32:29 > 0:32:33Sperm whales all across the Gulf of Alaska are now learning
0:32:33 > 0:32:35the trick from each other.
0:32:36 > 0:32:40There are at least 120 of them targeting the black cod boats
0:32:40 > 0:32:42and raiding their lines.
0:32:44 > 0:32:45And more are coming in every year.
0:32:52 > 0:32:55In Alaska, nature's riches are abundant,
0:32:55 > 0:32:58but sometimes you have to fight for them.
0:33:06 > 0:33:10The weeks are slipping by and the sun is getting stronger.
0:33:17 > 0:33:20In the southern forest, the black bear cubs are growing fast.
0:33:22 > 0:33:24But mum's reserves are running low.
0:33:33 > 0:33:37It seems like a lot of effort for not much reward,
0:33:37 > 0:33:39but she'll eat whatever she can get.
0:33:44 > 0:33:46Up in the tundra, there's been a baby boom
0:33:46 > 0:33:48of arctic ground squirrels.
0:33:50 > 0:33:53Each baby has grown ten times bigger in just over a month.
0:33:58 > 0:34:01A family of Lapland longspur chicks is eating anything
0:34:01 > 0:34:03the parents can rustle up.
0:34:03 > 0:34:05CHICK SQUEAKS
0:34:05 > 0:34:08They'll be fledging when they're only eight days old.
0:34:11 > 0:34:14Everything here is in a race to grow.
0:34:14 > 0:34:16CHICKS CHIRP
0:34:22 > 0:34:25A caribou baby is on its feet the day it's born,
0:34:25 > 0:34:28ready to join the vast herds up to a million strong.
0:34:35 > 0:34:38Spring might have arrived late, but now it's in rush.
0:34:44 > 0:34:47The sun punches higher and higher as the days lengthen
0:34:47 > 0:34:49and the ground warms.
0:34:55 > 0:34:58But not even the sun at its strongest
0:34:58 > 0:35:00can take away every speck of ice.
0:35:14 > 0:35:17Great icy glaciers.
0:35:19 > 0:35:21They scrape across the land,
0:35:21 > 0:35:24picking up thousands of tonnes of shattered rocks and boulders.
0:35:26 > 0:35:30Debris that is vital to the next stage of spring.
0:35:35 > 0:35:39These flecks of ancient rock - rich in minerals -
0:35:39 > 0:35:41lie deep inside the glacier.
0:35:43 > 0:35:45For now, they are trapped.
0:35:50 > 0:35:54But under the glare of the sun, the dense blue ice begins to melt.
0:36:05 > 0:36:08Little trickles of water slide under the glacier.
0:36:16 > 0:36:19Trickles become streams,
0:36:19 > 0:36:22and streams become rivers,
0:36:22 > 0:36:25cutting their way through the heart of the ice.
0:36:40 > 0:36:42When they finally reach the glacier's edge,
0:36:42 > 0:36:44they cascade to the ground.
0:36:47 > 0:36:51300 billion tonnes of meltwater.
0:37:01 > 0:37:04The water that has carried the minerals from far inland
0:37:04 > 0:37:07now delivers them directly to the sea.
0:37:14 > 0:37:17A giant plume of silt slides from the land,
0:37:17 > 0:37:20spreading the richness all along the southern coast.
0:37:23 > 0:37:27With the sea full of sunlight and flushed with nutrients...
0:37:28 > 0:37:32..the Alaskan spring is about to deliver its greatest bounty.
0:37:36 > 0:37:37Nature's gold rush.
0:37:41 > 0:37:45First to arrive are herring in their billions.
0:37:48 > 0:37:51The richness of the water is what's brought them here.
0:37:53 > 0:37:56But they soon attract attention by their sheer numbers.
0:38:03 > 0:38:04Sea lions.
0:38:27 > 0:38:30Pacific white-sided dolphins join the chase.
0:38:38 > 0:38:42The herring on the edges of the shoal don't have a chance.
0:38:42 > 0:38:45They're attacked from all sides.
0:38:45 > 0:38:47Diving birds snatch them from below.
0:38:52 > 0:38:54Herring gulls reach down from above.
0:39:00 > 0:39:04The fish are now trapped against the surface with nowhere to go.
0:39:20 > 0:39:22Plenty of herring manage to escape.
0:39:22 > 0:39:27But even those that do get away have a much bigger hurdle ahead of them.
0:39:29 > 0:39:32'This is the Alaska Department of Fish and Game, the fishery will
0:39:32 > 0:39:35'occur in approximately two minutes, two minutes.'
0:39:37 > 0:39:40This annual herring run brings out every boat in the bay.
0:39:42 > 0:39:46But the law says you can only fish for a very short time.
0:39:47 > 0:39:49'25 seconds, stand by for countdown.'
0:39:50 > 0:39:53Spotter planes line up the fishermen
0:39:53 > 0:39:56and the boats jostle for the best positions.
0:39:59 > 0:40:02- Here in Sitka...- 'Ten...' - ..it's game on.
0:40:02 > 0:40:04'..nine...
0:40:04 > 0:40:05'eight...
0:40:05 > 0:40:10'seven, six, five,
0:40:10 > 0:40:14'four, three,
0:40:14 > 0:40:19'two, one...
0:40:19 > 0:40:20'Open!'
0:40:31 > 0:40:34They might only get 15 minutes to catch what they can.
0:40:37 > 0:40:40But if they play it right, they'll catch 1,000 tonne of fish.
0:40:43 > 0:40:46You can make your year's salary in a day.
0:40:46 > 0:40:48It's that big a deal.
0:41:04 > 0:41:08Every year, 20 million-worth of herring are pulled out of the sea.
0:41:13 > 0:41:16But this is only a fraction of the total numbers.
0:41:27 > 0:41:31As the fishermen draw in their nets, the escapees rush to the shallows,
0:41:31 > 0:41:34but there's a final barrier in their path...
0:41:36 > 0:41:39A wall of bubbles.
0:41:41 > 0:41:45These bubbles may seem more fragile than a fishing net,
0:41:45 > 0:41:47but they are just as deadly.
0:42:04 > 0:42:06Humpback whales.
0:42:06 > 0:42:10Only half a mile from where the fishermen are working,
0:42:10 > 0:42:14a pod of humpbacks are also working the herring bonanza.
0:42:14 > 0:42:16But their secret is teamwork.
0:42:23 > 0:42:24The lead dives first.
0:42:27 > 0:42:30Then the rest of the pod follow one by one.
0:42:38 > 0:42:42As they descend, they blow out a curtain of bubbles.
0:42:42 > 0:42:45WHALE VOCALISES
0:42:52 > 0:42:56WHALE VOCALISES
0:42:56 > 0:42:58The herring are spooked
0:42:58 > 0:43:01and they bunch into a desperate little circle.
0:43:02 > 0:43:03The trap is set.
0:43:05 > 0:43:07WHALE VOCALISES
0:43:12 > 0:43:14Their timing is perfect.
0:43:23 > 0:43:27'Ten, nine, eight, seven...'
0:43:27 > 0:43:30For the fishermen of Sitka, their time's up.
0:43:30 > 0:43:34'..five, four, three, two, one, closed!'
0:43:38 > 0:43:41But the humpbacks can carry on round the clock,
0:43:41 > 0:43:43each catching a tonne of fish a day.
0:43:54 > 0:43:58For two frantic weeks of spring, the herring run draws in fishermen
0:43:58 > 0:44:00and wildlife to these rich bays.
0:44:04 > 0:44:08People have been harvesting the seas here for 14,000 years...
0:44:10 > 0:44:13..ever since the first settlers arrived.
0:44:25 > 0:44:29Spring in the south is especially significant for Harvey,
0:44:29 > 0:44:31a member of the Kaagwaantaan clan.
0:44:34 > 0:44:39Right now, when it gets to this point and the weather starts warming,
0:44:39 > 0:44:46you tend to watch what is happening with the weather and the land
0:44:46 > 0:44:48and the things around us.
0:44:51 > 0:44:57This specific area has been very special to a lot of Alaskan natives.
0:44:58 > 0:45:01The ocean and the lands around it provided for our people.
0:45:03 > 0:45:07For thousands and thousands of years, the herring have been coming here.
0:45:08 > 0:45:12All he needs are hemlock branches for his harvest
0:45:12 > 0:45:15because Harvey knows the secret of the herring's arrival.
0:45:17 > 0:45:21They're not feeding in these nutrient-rich waters.
0:45:21 > 0:45:23The herring are here to spawn.
0:45:25 > 0:45:28But first, he and his family have to find them.
0:45:33 > 0:45:35It's all about looking for the signs.
0:45:42 > 0:45:48I know my father said the seagulls were the ones that named the herring.
0:45:48 > 0:45:49They started calling.
0:45:51 > 0:45:53They'd say, "Yah, yah, yah!"
0:45:54 > 0:45:57And that's usually when they saw herring.
0:45:57 > 0:45:59They'd said the herring are coming.
0:46:01 > 0:46:03The whales seem to agree.
0:46:03 > 0:46:07That's another sign that they're in the right place at the right time.
0:46:08 > 0:46:10WHALE SHOOTS OUT AIR
0:46:10 > 0:46:12Ah!
0:46:12 > 0:46:13Ha-ha!
0:46:15 > 0:46:16Time to set the trap.
0:46:20 > 0:46:21Throw it in, Dale.
0:46:29 > 0:46:32The hemlock leaves are strong and dense,
0:46:32 > 0:46:35the perfect place for the herring to lay their eggs.
0:46:40 > 0:46:43All they can do now is hope they have timed it right.
0:46:54 > 0:46:57Early the next day, the herring arrive in the shallows.
0:47:00 > 0:47:04Straight away, they begin to lay on every surface
0:47:04 > 0:47:06including Harvey's hemlock branches.
0:47:10 > 0:47:13Millions and millions of eggs
0:47:13 > 0:47:15pounced on by hundreds of hungry mouths.
0:47:22 > 0:47:25The spawn is so thick it changes the colour of the sea.
0:47:29 > 0:47:34In three days, 800 billion eggs are laid along this coastline.
0:47:38 > 0:47:40As the tide goes out,
0:47:40 > 0:47:44a frosting of tiny eggs is left sparkling like jewels in the sun.
0:47:52 > 0:47:55Harvey and his family have come back to their hemlock branches.
0:47:57 > 0:48:00HE HEAVES
0:48:00 > 0:48:03The branches are so thick with eggs,
0:48:03 > 0:48:05they can barely lift them from the water.
0:48:16 > 0:48:19Harvey's family will share the herring roe with native communities
0:48:19 > 0:48:21right across Alaska.
0:48:23 > 0:48:26But they'll start with their nearest and dearest.
0:48:26 > 0:48:28Do you think Mom will like it?
0:48:28 > 0:48:30I think Mom will really like it!
0:48:33 > 0:48:36Finally, spring has paid dividends.
0:48:36 > 0:48:38To those Alaskans that have timed it right,
0:48:38 > 0:48:41the rewards have been generous.
0:48:44 > 0:48:47The sun has transformed Alaska,
0:48:47 > 0:48:49hustling out winter
0:48:49 > 0:48:51and bringing back the good times.
0:48:59 > 0:49:02Everywhere is full of life
0:49:02 > 0:49:03and colour.
0:49:06 > 0:49:09The starving time is finally over.
0:49:11 > 0:49:15Those that struggled in the early days of spring are now cashing in.
0:49:25 > 0:49:28But the sun's return has only just begun.
0:49:30 > 0:49:3524 hours of daylight will bring a whole new set of challenges.
0:49:35 > 0:49:38And a new cast of characters ready to face them.
0:49:41 > 0:49:42BEARS GROWL
0:49:42 > 0:49:46For better or worse, the Alaskan summer is on its way.
0:50:03 > 0:50:05Of all the stories from wild Alaska,
0:50:05 > 0:50:08the most intriguing came from the fishermen of Sitka.
0:50:11 > 0:50:15They told us about a story of giant ocean predators -
0:50:15 > 0:50:1950-tonne sperm whales - that were targeting their catch of black cod.
0:50:24 > 0:50:27The times that are really tough is when you get
0:50:27 > 0:50:29eight to ten of them on you...
0:50:29 > 0:50:31You don't stand a chance.
0:50:31 > 0:50:33They'll rip every single fish off your hook.
0:50:36 > 0:50:40The whale just comes up and puts its mouth on your ground line.
0:50:40 > 0:50:42When the line is coming up like that, it just strips your black cod
0:50:42 > 0:50:44right off the hooks.
0:50:44 > 0:50:50There's been sets where I should've had 300-400 cod,
0:50:50 > 0:50:53and, like, this last trip we had, I think, four.
0:50:53 > 0:50:55It drives you absolutely mad.
0:50:57 > 0:50:59I think the problem is getting worse,
0:50:59 > 0:51:01definitely getting worse.
0:51:11 > 0:51:16One fishermen, Stephen Rhoads, has been fishing here for 20 years
0:51:16 > 0:51:19and he knows this story only too well.
0:51:19 > 0:51:21I don't know how to quantify their intelligence,
0:51:21 > 0:51:26but their effectiveness is almost perfect.
0:51:26 > 0:51:30They're getting better at this every single year
0:51:30 > 0:51:34and it's less work for them to hang out with us and take our fish
0:51:34 > 0:51:36than it is to dive down and get them off the bottom.
0:51:36 > 0:51:40There's no doubt that these creatures are very smart.
0:51:43 > 0:51:45The camera team spent a week with Stephen and his crew
0:51:45 > 0:51:47as they set out to fish.
0:51:49 > 0:51:52And it doesn't take long before they see first hand
0:51:52 > 0:51:55the extraordinary damage to his catch.
0:51:55 > 0:51:56Coming in.
0:52:00 > 0:52:01Broken ganion.
0:52:03 > 0:52:04Broken ganion.
0:52:05 > 0:52:06I feel like when the line jumps
0:52:06 > 0:52:10you can feel the whales tugging fish off the hooks.
0:52:11 > 0:52:13They're better predators than we are, man.
0:52:15 > 0:52:17That's for sure. They're good at what they do.
0:52:19 > 0:52:23The team's role was to film this extraordinary problem,
0:52:23 > 0:52:25but they soon found themselves caught up
0:52:25 > 0:52:27in Stephen's determined quest.
0:52:28 > 0:52:32He wants to find a long-term solution to this problem.
0:52:32 > 0:52:35We're not trying to get rid of the whales,
0:52:35 > 0:52:39we're trying to find a way where they can have their natural prey
0:52:39 > 0:52:41and we can fish.
0:52:41 > 0:52:45And by hanging out with really smart people,
0:52:45 > 0:52:49we can find a way to get back to where we can both make a living.
0:52:54 > 0:52:57The smart people are a group of whale scientists.
0:52:59 > 0:53:01Their investigation has been going on -
0:53:01 > 0:53:04above and below the water - for ten years.
0:53:07 > 0:53:11And they've already tried a few things to lure the whales away.
0:53:14 > 0:53:18We've used some sound deterrents and it did work briefly,
0:53:18 > 0:53:24but they're such an intelligent species that they figured it out
0:53:24 > 0:53:28pretty quickly. It wasn't as effective as everyone hoped.
0:53:29 > 0:53:32There clearly aren't any easy solutions.
0:53:35 > 0:53:38The scientists now have to come up with another plan
0:53:38 > 0:53:41to better understand the whales' movements.
0:53:43 > 0:53:46Maybe satellite tags would help show where they were.
0:53:46 > 0:53:48Then at least the fishermen could avoid them.
0:53:51 > 0:53:52Oh, right there.
0:53:55 > 0:53:58But after a week at sea, they've only tagged three.
0:53:59 > 0:54:03There are 120 whales on this coastline...
0:54:04 > 0:54:07..and the scientists simply don't have the resources to tag them all.
0:54:10 > 0:54:14One of these is a new whale for us. It's not in our catalogue.
0:54:15 > 0:54:18Yeah, they're becoming smarter and smarter.
0:54:18 > 0:54:20It seems like their numbers are increasing.
0:54:22 > 0:54:25The number of whales around is bad news for the fishermen
0:54:25 > 0:54:27but good news for the film crew.
0:54:28 > 0:54:31It's never easy working on boats at the best of times,
0:54:31 > 0:54:35and the supersize camera gear is hard to handle.
0:54:35 > 0:54:38- A little wobbly, right? - Yeah. Getting my sea legs.
0:54:46 > 0:54:49They are starting to capture shots of the whales
0:54:49 > 0:54:51as they sneak around the boat.
0:54:52 > 0:54:55But the real action was happening beneath the waves.
0:55:05 > 0:55:08The team decide to take the risk of sending down
0:55:08 > 0:55:10some of their tiny underwater cameras.
0:55:11 > 0:55:16Time-triggered, pressure-tested, and sealed in water-tight housing,
0:55:16 > 0:55:19it's the only way they are going to see what's going on down there.
0:55:24 > 0:55:25All set?
0:55:25 > 0:55:28Each camera is attached to the fishermen's lines.
0:55:36 > 0:55:40At 80m down, darkness takes over.
0:55:40 > 0:55:42It's only the lights on the cameras
0:55:42 > 0:55:44that allow them to see anything at all.
0:55:48 > 0:55:50A further half-mile down,
0:55:50 > 0:55:54they hit the seabed and start capturing this alien world.
0:55:58 > 0:56:01The water's just above freezing.
0:56:01 > 0:56:03The pressure is immense.
0:56:03 > 0:56:06And the inhabitants seem less than friendly.
0:56:10 > 0:56:12And then, amidst the darkness,
0:56:12 > 0:56:15the distant clicking of sperm whales searching for prey.
0:56:21 > 0:56:25Eight hours later, the cameras are hauled back up.
0:56:25 > 0:56:26But the big question is -
0:56:26 > 0:56:30did they capture anything that would shed any light on the behaviour?
0:56:30 > 0:56:31Camera.
0:56:36 > 0:56:37Barely made it.
0:56:42 > 0:56:45The team have captured 50 hours of deep-sea footage.
0:56:47 > 0:56:50But the cunning whales have completely avoided
0:56:50 > 0:56:52being caught on camera.
0:56:52 > 0:56:54- Nothing.- Nothing.
0:56:54 > 0:56:56It's like fishing.
0:56:56 > 0:56:59In spite of everyone's best efforts,
0:56:59 > 0:57:03this extraordinary behaviour is still frustratingly hard to see.
0:57:09 > 0:57:11After a week of filming and years of research,
0:57:11 > 0:57:15to this day, there is only one single shot of a sperm whale
0:57:15 > 0:57:17stealing fish off the longline,
0:57:17 > 0:57:20filmed years ago by the scientists themselves.
0:57:22 > 0:57:24The whales are outsmarting everyone.
0:57:25 > 0:57:27It's not going our direction.
0:57:27 > 0:57:31The whales are a bigger problem every year
0:57:31 > 0:57:33and there isn't a solution yet.
0:57:34 > 0:57:37Even though we sit right on top of the surface of the water
0:57:37 > 0:57:41and try to look down in the deeps with our equipment,
0:57:41 > 0:57:43and we bring a few fish up,
0:57:43 > 0:57:46there is a lot more going on down there than we totally know about.
0:57:50 > 0:57:54The team have witnessed the whales' extraordinary behaviour.
0:57:55 > 0:57:59The collaboration between fishermen and scientists continues.
0:57:59 > 0:58:02Perhaps one day they'll find a way to resolve
0:58:02 > 0:58:03this riddle of the deep.
0:58:09 > 0:58:11Next time...
0:58:11 > 0:58:13Summer arrives in Alaska,
0:58:13 > 0:58:17bringing with it the bounty that everyone has been waiting for.
0:58:19 > 0:58:21But they'll need to cash in quick.
0:58:23 > 0:58:25The days may be long but the season is short.
0:58:26 > 0:58:28And the good times won't last forever.