0:00:36 > 0:00:38The coast.
0:00:38 > 0:00:41Nature's most demanding hunting ground.
0:00:49 > 0:00:53So hazardous that few predators stay here all year.
0:01:03 > 0:01:08This frontier between sea and land is continuously changing.
0:01:17 > 0:01:20Opportunities never last long.
0:01:23 > 0:01:28To hunt at the coast, you have to be in the right place
0:01:28 > 0:01:30at just the right time.
0:01:46 > 0:01:51On the east coast of America, in the tidal creeks of South Carolina,
0:01:51 > 0:01:56a team of hunters is about to leave the safety of their natural habitat.
0:02:18 > 0:02:22This group of bottlenose dolphins has perfected
0:02:22 > 0:02:24a unique hunting strategy.
0:02:27 > 0:02:32It relies on teamwork, intelligence and timing.
0:02:42 > 0:02:47But beaching themselves like this is also difficult and dangerous.
0:03:06 > 0:03:10Hunting is only possible for three hours around low tide,
0:03:10 > 0:03:12when the mud banks are exposed.
0:03:17 > 0:03:22Razor-sharp oysters cover much of the shore.
0:03:22 > 0:03:24Beaching here could be lethal.
0:03:35 > 0:03:37The hunters need to find a stretch of shoreline
0:03:37 > 0:03:39with just the right slope.
0:03:42 > 0:03:45Too level and the dolphins risk stranding.
0:03:50 > 0:03:54Too steep and they can't force their prey from the water.
0:04:06 > 0:04:10Working as a team, the dolphins surround the fish,
0:04:10 > 0:04:12driving them towards the shore.
0:04:35 > 0:04:39Attacking in perfect synchrony, the dolphins create a bow wave.
0:04:46 > 0:04:49It carries their prey onto the muddy banks.
0:05:03 > 0:05:06Other fish-eaters profit from their daring.
0:05:12 > 0:05:15Herons and gulls follow every hunt.
0:05:27 > 0:05:29To get to the fish first,
0:05:29 > 0:05:32the dolphins drive themselves high up the bank.
0:05:33 > 0:05:36But if they go too far, they risk stranding.
0:05:50 > 0:05:52To prevent fish escaping between them,
0:05:52 > 0:05:56the dolphins all beach themselves on the same side.
0:05:59 > 0:06:01Always the right.
0:06:03 > 0:06:05But this has a cost -
0:06:05 > 0:06:09each time they grab a fish, they also take in a mouthful of mud.
0:06:12 > 0:06:15The grit gradually wears down their teeth...
0:06:20 > 0:06:21..but on one side only.
0:06:27 > 0:06:32In time, these teeth get so worn down that older dolphins can no
0:06:32 > 0:06:36longer hunt like this and must find other ways to catch fish.
0:06:51 > 0:06:56Within a few hours, the banks will vanish once again
0:06:56 > 0:06:58beneath the muddy water.
0:07:04 > 0:07:08The ebb and flow of the tide dominates the lives of all
0:07:08 > 0:07:11who try to hunt on the coast.
0:07:22 > 0:07:26Northern Australia has the highest tides in the tropics,
0:07:26 > 0:07:29which expose vast areas of shoreline.
0:07:34 > 0:07:38And here lives a truly extraordinary species of octopus.
0:07:50 > 0:07:55Octopuses are marine animals - they live and breathe underwater.
0:08:02 > 0:08:07At low tide, most octopuses would be imprisoned in their rocky pools.
0:08:13 > 0:08:17But this is no ordinary octopus.
0:08:49 > 0:08:54It's the only one specially adapted to walk on land.
0:08:56 > 0:08:58It pulls itself along,
0:08:58 > 0:09:02using the hundreds of tiny suckers that line its arms.
0:09:08 > 0:09:12Hunting for crabs, it walks from pool to pool.
0:09:24 > 0:09:26Apart from a rather startled fish...
0:09:31 > 0:09:33..this one is empty.
0:09:43 > 0:09:45So the octopus moves on.
0:10:03 > 0:10:06A rock pool may seem like a safe refuge.
0:10:13 > 0:10:17But the octopus' suckers enable it to move
0:10:17 > 0:10:20just as stealthily in water as out of it.
0:10:44 > 0:10:47CRUNCHING
0:11:00 > 0:11:04Nowhere is safe when this octopus is around.
0:11:09 > 0:11:13Everything living here must march to the rhythm of the coast.
0:11:43 > 0:11:47Regiments of soldier crabs, several thousand strong,
0:11:47 > 0:11:52march and counter-march across these Australian beaches.
0:12:02 > 0:12:05They sift out microscopic food.
0:12:05 > 0:12:09But they can only feed for a few hours while the sand remains damp.
0:12:15 > 0:12:19And it's not just the tide they're racing against.
0:12:24 > 0:12:27Hunting birds follow in their wake.
0:12:29 > 0:12:32But the army is undeterred.
0:12:41 > 0:12:43They swarm in such huge numbers
0:12:43 > 0:12:46that their predators make little impact upon them.
0:12:50 > 0:12:54But safety in numbers isn't the only defence on these flats.
0:12:58 > 0:13:02Another crab here has a different strategy.
0:13:02 > 0:13:05The sand bubbler crab - no bigger than a pea.
0:13:08 > 0:13:11They also sift out tiny food particles
0:13:11 > 0:13:15and then leave the sand as pellets in their wake.
0:13:20 > 0:13:25Sand bubblers are wary and never venture far from their burrows.
0:13:30 > 0:13:33The crabs position their sand balls very carefully
0:13:33 > 0:13:36to ensure there is a clear path back to safety.
0:14:03 > 0:14:06As soon as the coast is clear, they're off again,
0:14:06 > 0:14:09racing to feed before the sand dries out.
0:14:26 > 0:14:30The industry of thousands transforms the whole beach...
0:14:38 > 0:14:40..until the tide returns once more.
0:14:45 > 0:14:49Few hunters make the coast their permanent home -
0:14:49 > 0:14:54most only visit to take advantage of short-lived opportunities.
0:15:00 > 0:15:02On the coast of Thailand,
0:15:02 > 0:15:07a most unlikely visitor waits for the tide to ebb.
0:15:21 > 0:15:27Long-tailed macaques feed mostly on fruit and leaves in the forest.
0:15:28 > 0:15:33But these have learnt to supplement their vegetarian diet with seafood.
0:15:38 > 0:15:41As the tide begins to fall, the macaques make their way
0:15:41 > 0:15:45down to the shore - a beach-side restaurant is about to open.
0:15:58 > 0:16:02There's plenty of food here, if you know how to get at it.
0:16:08 > 0:16:12The macaques have learnt to use heavy rocks as tools
0:16:12 > 0:16:14to break open the sea snails.
0:16:17 > 0:16:21It takes a great deal of skill to master this technique,
0:16:21 > 0:16:25but not everyone has got the hang of it.
0:16:56 > 0:17:00You have to be ingenious to make a living at the coast.
0:17:02 > 0:17:07As the tide falls still further, it reveals the next course.
0:17:12 > 0:17:14To feed on this dish,
0:17:14 > 0:17:17they need a stone tool with a very particular shape.
0:17:19 > 0:17:21They're after rock oysters.
0:17:28 > 0:17:31To crack the shells open, they must strike the oyster
0:17:31 > 0:17:34in just the right place with their chosen tool.
0:17:51 > 0:17:56The lowest tide reveals a course that is particularly delicious...
0:17:59 > 0:18:01..but also very hard to collect.
0:18:14 > 0:18:19Crabs have good eyesight and can move fast.
0:18:19 > 0:18:23So catching them requires a special trick.
0:18:29 > 0:18:33Before pouncing, the macaques wait for a wave to obscure their attack.
0:18:53 > 0:18:56Macaques learn their skills by watching their parents.
0:19:04 > 0:19:08But some techniques do take time to perfect.
0:19:26 > 0:19:30And time and tide waits for no macaque.
0:19:41 > 0:19:46The returning water closes the beach restaurant for another day.
0:19:59 > 0:20:02It's not just tides that rule the lives
0:20:02 > 0:20:03of those that live on the coast.
0:20:09 > 0:20:11The shores of Chile are battered
0:20:11 > 0:20:15by some of the wildest and coldest seas.
0:20:21 > 0:20:25This coastline is home to a remarkable little hunter...
0:20:32 > 0:20:35..the South American marine otter.
0:20:37 > 0:20:40The world's smallest sea mammal.
0:20:45 > 0:20:50This rare and elusive otter is half the size of its European cousin.
0:21:02 > 0:21:05They live along the Pacific coast of South America,
0:21:05 > 0:21:09right down to Cape Horn at the very tip of the continent.
0:21:14 > 0:21:16Surprisingly, the pounding breakers
0:21:16 > 0:21:20aren't a problem for the little otters...
0:21:21 > 0:21:23..but the cold water is.
0:21:27 > 0:21:32A continuous frigid current sweeps up from Antarctica.
0:21:41 > 0:21:46A small body loses heat faster than a large one, and so these tiny
0:21:46 > 0:21:51otters can only hunt in the chilly water for 20 minutes at a time.
0:21:56 > 0:22:00But their small size enables them to reach the fish and crabs
0:22:00 > 0:22:02that hide amongst the boulders.
0:22:15 > 0:22:20To stay warm, marine otters have to eat a quarter of their body weight
0:22:20 > 0:22:23in seafood every single day.
0:22:31 > 0:22:33And things are particularly hard for this female
0:22:33 > 0:22:38because her cubs aren't yet old enough to hunt for themselves.
0:22:50 > 0:22:54Before each fishing trip she rolls in seaweed,
0:22:54 > 0:22:56trapping air in her fur,
0:22:56 > 0:23:00so insulating herself from the chill of the seas.
0:23:08 > 0:23:10The cold isn't her only challenge.
0:23:14 > 0:23:17Being so small, these otters can only hold their breath
0:23:17 > 0:23:22for about a minute, making every dive a race against time.
0:23:31 > 0:23:35This otter lives on a calorific knife-edge,
0:23:35 > 0:23:39often only getting enough from one hunting trip to fuel the next.
0:24:22 > 0:24:25Success - a meal for the youngsters.
0:24:42 > 0:24:46These otters spend their entire lives at the coast,
0:24:46 > 0:24:50so they must accept its day-to-day challenges.
0:24:50 > 0:24:55But coasts pulse to much more than just the daily rhythms.
0:25:20 > 0:25:22On the shores of Alaska,
0:25:22 > 0:25:26a spectacular annual event is about to take place.
0:25:30 > 0:25:36Each July, predators gather for the biggest feast of the year...
0:25:36 > 0:25:39but it will only last a few weeks.
0:25:45 > 0:25:48Brown bears come down from the hills.
0:25:53 > 0:25:55Wolves appear out of the woods.
0:25:57 > 0:25:59And seals assemble in the ocean.
0:26:02 > 0:26:05The coast is the only place where hunters from the sea
0:26:05 > 0:26:08meet those from land and air.
0:26:11 > 0:26:16Bears have a sense of smell 2,000 times better than ours
0:26:16 > 0:26:19and can even detect prey out at sea.
0:26:22 > 0:26:25They know the salmon are coming.
0:26:28 > 0:26:31BARKING
0:26:31 > 0:26:34They also know the best fishing spots...
0:26:35 > 0:26:38..and are prepared to fight for them.
0:26:44 > 0:26:46GROWLING
0:26:56 > 0:26:58GROWLING
0:27:09 > 0:27:12After years feeding out in the Pacific,
0:27:12 > 0:27:16the salmon are returning to spawn.
0:27:16 > 0:27:17But before they head upriver,
0:27:17 > 0:27:22they must pause and modify their bodies to function in fresh water.
0:27:32 > 0:27:35The young and overeager try to catch the salmon
0:27:35 > 0:27:37while they're still in the surf.
0:27:39 > 0:27:43Those with experience are more patient.
0:27:48 > 0:27:51After six months of starvation in a winter den,
0:27:51 > 0:27:55all this food is just too tempting for the youngster.
0:28:14 > 0:28:18Wise old bears wait for the salmon to move into the river,
0:28:18 > 0:28:21where they know the fishing will be easier.
0:28:25 > 0:28:28The incoming tide signals a change.
0:28:32 > 0:28:36The experienced bears now take up their prized fishing spots
0:28:36 > 0:28:38at the mouth of the river.
0:28:40 > 0:28:43The salmon are finally here.
0:28:47 > 0:28:50As the fish are funnelled into shallower water,
0:28:50 > 0:28:52a seal gets its chance.
0:29:22 > 0:29:24The wolves will have to wait.
0:29:27 > 0:29:29Bears dominate the river-mouth.
0:29:59 > 0:30:01These bears rely on the salmon run
0:30:01 > 0:30:05for nearly 90% of their year's food.
0:30:11 > 0:30:15Most of the salmon make it upstream past the bears,
0:30:15 > 0:30:19but now they must run the gauntlet of wolves.
0:30:56 > 0:31:01The salmon will sustain the wolves through the rest of the summer.
0:31:04 > 0:31:08The sheer abundance of this seasonal bounty
0:31:08 > 0:31:12has made these bears the largest in North America.
0:31:21 > 0:31:26Estuaries are the meeting place of rivers and sea,
0:31:26 > 0:31:30and they're vital staging points for migrating birds.
0:31:33 > 0:31:38In Europe, each autumn, they're visited by millions of waders.
0:31:42 > 0:31:45The birds are returning from their breeding grounds in the Arctic
0:31:45 > 0:31:50to overwinter in Africa, and are stopping off to refuel.
0:31:56 > 0:32:00Knot can only feed when the mudflats are exposed.
0:32:02 > 0:32:05At high tide, they're forced onshore
0:32:05 > 0:32:09where they must wait for the tide to turn and reopen the larder.
0:32:19 > 0:32:21A peregrine falcon.
0:32:28 > 0:32:30BIRDS SQUAWK
0:32:40 > 0:32:44Young peregrines come to these estuaries in autumn...
0:32:44 > 0:32:46to hunt waders.
0:32:48 > 0:32:52Peregrines are the world's fastest aerial hunters,
0:32:52 > 0:32:56but this is a very challenging environment for a young falcon.
0:32:59 > 0:33:03It's one predator faced with thousands of prey.
0:33:08 > 0:33:09Flashing black and white,
0:33:09 > 0:33:14the swirling mass of wings dazzles the falcon's sensitive eyesight.
0:33:39 > 0:33:43An individual target may be a better option.
0:33:54 > 0:33:58A peregrine's plumage is not properly waterproof,
0:33:58 > 0:34:00so he can't afford to get his feathers wet.
0:34:02 > 0:34:05He must flush his prey into the air.
0:34:13 > 0:34:14But as soon as he gets close,
0:34:14 > 0:34:18the waders ditch into the sea where he can't follow.
0:34:47 > 0:34:52Success depends on keeping his prey away from the water.
0:34:57 > 0:35:00Now it's a dogfight at close quarters.
0:35:33 > 0:35:36Peregrines only stay around estuaries
0:35:36 > 0:35:38for the few months the waders are there.
0:35:38 > 0:35:42As soon as their prey leaves, they will head back inland.
0:35:52 > 0:35:55Some animals come to the coast, not to feed
0:35:55 > 0:35:57but to have their young.
0:36:10 > 0:36:12SEA LION CALLS
0:36:13 > 0:36:15Patagonian sea lions.
0:36:17 > 0:36:19These are just a few months old.
0:36:28 > 0:36:31Sea lions can't give birth at sea,
0:36:31 > 0:36:33they must come to land to have their pups.
0:36:40 > 0:36:43Each summer, thousands cluster in colonies
0:36:43 > 0:36:46along Argentina's Valdes Peninsula.
0:36:53 > 0:36:56The mothers regularly return to sea to hunt...
0:36:57 > 0:36:59..but their young stay on the beach
0:36:59 > 0:37:01for they have not yet learnt to swim.
0:37:28 > 0:37:31Orca. Killer whales.
0:37:34 > 0:37:38They come at exactly the same time each year to hunt the pups.
0:37:44 > 0:37:47It's a narrow window of opportunity
0:37:47 > 0:37:51and the odds are stacked against the hunters.
0:38:00 > 0:38:01Just like the dolphins,
0:38:01 > 0:38:05orca take great risks in leaving their natural habitat.
0:38:12 > 0:38:15With every attack, there's a real danger of being stranded.
0:38:34 > 0:38:37Orca can only hunt for a few hours each day,
0:38:37 > 0:38:43because at low tide a rocky reef blocks their access to the beach.
0:38:49 > 0:38:54So until the tide is high, the pups are safe.
0:39:00 > 0:39:04Early in the season the orca have one big advantage...
0:39:06 > 0:39:10..the pups are naive and don't yet recognise the whales as a threat.
0:39:17 > 0:39:20But the young sea lions will learn quickly.
0:39:25 > 0:39:29Silently, the killer whales move into position.
0:39:51 > 0:39:54Less than half the attacks are successful
0:39:54 > 0:39:57and with each attempt, the pups grow wiser.
0:40:00 > 0:40:04The orca's advantage is slipping away.
0:40:18 > 0:40:20For the next few weeks,
0:40:20 > 0:40:25hunter and hunted are locked in a desperate race...
0:40:26 > 0:40:29..the orca to seize pups,
0:40:29 > 0:40:32and the sea lions to learn how to evade their attacks.
0:41:29 > 0:41:32These young sea lions have triumphed.
0:41:32 > 0:41:37They've learnt to recognise the danger and evade the killers.
0:41:45 > 0:41:47For the orca,
0:41:47 > 0:41:51the window of opportunity has closed for another season.
0:42:01 > 0:42:03Newfoundland, Canada.
0:42:09 > 0:42:14A unique seasonal event is about to transform this place.
0:42:16 > 0:42:20It's the greatest coastal breeding spectacle on the planet,
0:42:20 > 0:42:23but it'll only last a week or two.
0:42:27 > 0:42:29Capelin.
0:42:29 > 0:42:30Billions of them.
0:42:34 > 0:42:39In early summer, these tiny fish mass just offshore.
0:42:45 > 0:42:47The great shoals inevitably attract predators.
0:42:53 > 0:42:55Humpback whales.
0:43:07 > 0:43:10They've travelled over 3,000 miles
0:43:10 > 0:43:13from their breeding grounds in the Caribbean.
0:43:14 > 0:43:16Nowhere else in the world
0:43:16 > 0:43:19do humpback whales gather to feed in greater numbers.
0:43:29 > 0:43:31But no sooner have the whales arrived
0:43:31 > 0:43:35than the capelin do something apparently suicidal.
0:43:49 > 0:43:52They deliberately cast themselves ashore,
0:43:52 > 0:43:56and, once out of water, they lay their eggs.
0:44:03 > 0:44:06They're one of only two species of fish
0:44:06 > 0:44:08that leave the ocean to spawn like this.
0:44:19 > 0:44:23A fish out of water is an easy meal.
0:44:26 > 0:44:29But capelin go to these extreme lengths
0:44:29 > 0:44:32to give their offspring the best chance of survival.
0:44:34 > 0:44:37For many, it's the ultimate sacrifice.
0:44:49 > 0:44:51Cod.
0:44:51 > 0:44:54Great numbers of them move in from deeper water
0:44:54 > 0:44:57to plunder this brief bounty.
0:45:02 > 0:45:05Their impact on the vast shoals is small
0:45:05 > 0:45:10but as they hunt, the cod drive capelin off the seabed
0:45:10 > 0:45:13and up into the range of the waiting humpbacks.
0:45:28 > 0:45:31The whales herd the fish against the cliffs.
0:45:46 > 0:45:49Then they unleash a secret weapon.
0:45:49 > 0:45:53WHALE SONG
0:46:04 > 0:46:08These bizarre calls panic the capelin,
0:46:08 > 0:46:12driving the fish ever closer together,
0:46:12 > 0:46:14making them a more concentrated target.
0:46:17 > 0:46:20WHALE SONG CONTINUES
0:46:26 > 0:46:29This bonanza will disperse within days,
0:46:29 > 0:46:32so the humpbacks have to make the most of it while they can.
0:46:37 > 0:46:43Hunters at the coast are always in a race against time.
0:47:38 > 0:47:42The Hunt team came to Chile to film the world's smallest sea mammal...
0:47:44 > 0:47:46..the South American marine otter.
0:47:49 > 0:47:50The thing about these otters
0:47:50 > 0:47:53is no-one really knows anything about them.
0:47:53 > 0:47:58No-one's actually studied them for any length of time at all.
0:47:58 > 0:48:00So Mark is going to have to work out
0:48:00 > 0:48:02the otters' movements and habits for himself.
0:48:06 > 0:48:08These otters have never been filmed before,
0:48:08 > 0:48:11but Mark has a lot of experience with British otters
0:48:11 > 0:48:13so it should be straightforward.
0:48:19 > 0:48:23Filming them underwater, however, is a daunting prospect -
0:48:23 > 0:48:25no-one has ever tried to dive with them.
0:48:27 > 0:48:31It's not going to be easy. Maybe one shot a day, two shots a day
0:48:31 > 0:48:33would be a successful trip.
0:48:34 > 0:48:37But the underwater team has a plan.
0:48:37 > 0:48:39Now, what we've got are these camouflaged wet suits,
0:48:39 > 0:48:41camouflage tape on the camera,
0:48:41 > 0:48:44just to try and help us to blend in a little bit more.
0:48:44 > 0:48:45And so does Mark.
0:48:45 > 0:48:48Well, you probably can't actually see me now, of course,
0:48:48 > 0:48:49covered in camo.
0:48:49 > 0:48:51But going to work, definitely going to work.
0:48:51 > 0:48:54Much better than Pearson's camo wetsuit palaver!
0:48:55 > 0:48:58Grown men dressed like that, it's ridiculous.
0:49:03 > 0:49:05We can't just get into the water and see them
0:49:05 > 0:49:06because they move too quickly.
0:49:06 > 0:49:09So I've got this little comms unit inside of my mask
0:49:09 > 0:49:11and I can listen to it underwater.
0:49:11 > 0:49:13and Joaquin can talk to me from the search unit.
0:49:13 > 0:49:15STATIC INTERFERENCE
0:49:15 > 0:49:16Oh, there's one.
0:49:21 > 0:49:23- JOAQUIN:- He's going west under rock one.
0:49:23 > 0:49:25I repeat, west under rock one.
0:49:28 > 0:49:31He's on the surface, swimming really fast to three.
0:49:33 > 0:49:36A combination of eyes on the surface...
0:49:38 > 0:49:40He's coming back to two.
0:49:40 > 0:49:44..and camouflage below brings early results.
0:49:47 > 0:49:52Filming otters underwater is turning out to be easier than Doug expected.
0:49:52 > 0:49:53That was cool.
0:49:53 > 0:49:56I wasn't sure we were going to see one of these guys underwater
0:49:56 > 0:49:57but, yeah, very encouraging.
0:49:59 > 0:50:01Success for the underwater team
0:50:01 > 0:50:03means the pressure is now on Mark.
0:50:06 > 0:50:09I've been here six-and-a-half hours
0:50:09 > 0:50:10and I've got one shot.
0:50:11 > 0:50:15Not very good shot of it on a rock over there.
0:50:15 > 0:50:16It's not going to work.
0:50:17 > 0:50:19It's not going to work like that.
0:50:23 > 0:50:26I think the only way that we're going to get any more
0:50:26 > 0:50:31is to find out a way of getting consistently close to them.
0:50:31 > 0:50:34I think the only way of doing that is at a den
0:50:34 > 0:50:39where there's cubs and they're coming back to it consistently.
0:50:41 > 0:50:46Surprisingly, the most likely den site is in a busy harbour.
0:50:48 > 0:50:51So we are just by the den of the otters
0:50:51 > 0:50:54and we are going to put the hide on location
0:50:54 > 0:50:57to hopefully get some shots of the otter up close.
0:51:00 > 0:51:03It's just a very weird mixture of, like, trying to hide from the animal
0:51:03 > 0:51:06when in fact it just sees people all the time.
0:51:08 > 0:51:09Doesn't quite add up.
0:51:11 > 0:51:14Right, well, you can just leave me in here now. I'm quite happy.
0:51:14 > 0:51:17Just send me down empanadas every few hours.
0:51:17 > 0:51:20See if you can have a word with the otters,
0:51:20 > 0:51:21tell them that dinner's up.
0:51:31 > 0:51:35I've been sat here now for three hours, looking at a rock.
0:51:40 > 0:51:42After a week of surveillance...
0:51:44 > 0:51:47Where's it gone, where is it, where is it, where is it?
0:51:47 > 0:51:51..Mark is no closer to figuring out any pattern
0:51:51 > 0:51:52in the otters' behaviour.
0:51:52 > 0:51:55Oh, don't do that.
0:51:55 > 0:51:59He's had only fleeting glimpses of the adults and no cubs.
0:52:05 > 0:52:07The weird thing is, I've filmed otters in Scotland
0:52:07 > 0:52:10and so I've been equating those otters with these otters.
0:52:10 > 0:52:13The more you find out about these otters,
0:52:13 > 0:52:16you realise that they're just not similar at all.
0:52:16 > 0:52:19All your tactics that you thought would work with otters
0:52:19 > 0:52:21are just straight out the window,
0:52:21 > 0:52:22so it's like starting again.
0:52:24 > 0:52:30News of another otter family nearby raises Mark's hopes.
0:52:30 > 0:52:31(It's going to happen.)
0:52:32 > 0:52:34The day starts out with promise.
0:52:37 > 0:52:40- ON RADIO:- 'I've just seen one of the cubs in the den.
0:52:41 > 0:52:44'Just for... It was about half a second.'
0:52:44 > 0:52:46That's great news. Over.
0:52:48 > 0:52:51But the sun brings out unwelcome visitors.
0:52:53 > 0:52:56Ah, yeah, there's been one around. About three hours ago,
0:52:56 > 0:53:02but a few people have turned up on the beach
0:53:02 > 0:53:03and we haven't seen it since.
0:53:08 > 0:53:12The topside shoot is proving to be much more difficult
0:53:12 > 0:53:14than anyone could have imagined.
0:53:15 > 0:53:17This is rather depressing
0:53:17 > 0:53:22because it's the only place that we have been able to actually see cubs.
0:53:25 > 0:53:29The big worry, really, is that the cubs are being moved
0:53:29 > 0:53:31from den to den.
0:53:31 > 0:53:33If they are being moved from den to den,
0:53:33 > 0:53:37then staking the dens out is almost impossible.
0:53:38 > 0:53:42Such are the challenges of trying to film an animal
0:53:42 > 0:53:44about which we know so little.
0:53:49 > 0:53:52With all their options exhausted,
0:53:52 > 0:53:56Mark and Ignacio dismantle their hide in the harbour.
0:53:56 > 0:54:00Wow! Wow!
0:54:00 > 0:54:03Oh, my... What the...?
0:54:03 > 0:54:07The hide that was supposed to be for Mark has been used by the otters.
0:54:07 > 0:54:09Look at his face!
0:54:16 > 0:54:17I can't believe it.
0:54:17 > 0:54:21They've been using the hide as a larder for their food.
0:54:25 > 0:54:28I've never felt so utterly defeated
0:54:28 > 0:54:30by an animal that I've tried to film.
0:54:32 > 0:54:38After two months, I still have no idea about these animals.
0:54:38 > 0:54:40Really no idea.
0:54:44 > 0:54:46I thought that was an otter, then!
0:54:52 > 0:54:57I just went to see in another cove this early morning,
0:54:57 > 0:55:01and I just found two little cubs playing in the water with one adult.
0:55:04 > 0:55:05What?
0:55:08 > 0:55:12We've finally got within 100 metres of a mother and cubs.
0:55:19 > 0:55:21Through sheer persistence,
0:55:21 > 0:55:25Mark finally gets his chance to film an otter family.
0:55:38 > 0:55:41You know, they don't feel like mammals,
0:55:41 > 0:55:42they're almost like little eels,
0:55:42 > 0:55:45you know, the way they disappear underneath the boulders.
0:55:47 > 0:55:49I think we've genuinely revealed something new about them -
0:55:49 > 0:55:51how they hunt.
0:55:51 > 0:55:52You know, they go through these rocks
0:55:52 > 0:55:54and that's why they're so small.
0:55:58 > 0:56:01What makes the otters successful hunters on this coast
0:56:01 > 0:56:04is also what makes them so hard to film...
0:56:06 > 0:56:10..they're small, fast and have an affinity for nooks and crannies.
0:56:15 > 0:56:16And Mark?
0:56:16 > 0:56:18He's finally learnt the secret
0:56:18 > 0:56:21to filming the world's smallest marine mammal.
0:56:23 > 0:56:24Keep the faith.
0:56:26 > 0:56:28Yeah, keep the faith.
0:56:32 > 0:56:35Next time, in the final episode,
0:56:35 > 0:56:38we examine the health of our planet's top predators.
0:56:42 > 0:56:45We meet the pioneers on the front line,
0:56:45 > 0:56:47searching for bold solutions.
0:56:50 > 0:56:54Can people make room for the world's most celebrated hunters?