The Big Blue - Ocean Stories from Down Under | Episode 1 | Free Documentary - Nature

The northern quarter of New Zealand's North Island is laced with harbours. They are all tidal and teeming with life. In these harbour habitats, the residents have evolved weird and wonderful adaptations to the tidal terrain. A family with a culture of compassion can transform into brutal predators, and a mother will lay down her life for her young. It's a spring morning in the beautiful Hokianga Harbour on Northland's west coast. The tide is full and the weather is calm. Waiting birds rest, waiting for the ebb tide to expose the riches, out of reach for now, in the mud and sand below. While the tide is high, fish gobble plankton in a magical underwater forest. A squadron of long-tailed stingrays advances inshore to forage for crustaceans. Their round bodies and undulating fins distinguish them from their smaller cousins, the eagle rays. They have more pointed fins, which they use like wings. Both ray species have barbed tails, which contain deadly venom for self-defence. But this morning, the usually graceful rays are skittish, and they have very good reason. This is an apex predator, a killer whale or orca. It has company. A pod of killer whales enters the mouth of the Hokianga Harbour. They're here for one thing, breakfast. These marine giants can grow up to nine metres long and must eat up to 230 kilograms every day. That's the equivalent of three average human adults. They've come to the right place. The Hokianga Harbour offers rich pickings, but hunting must wait. As they enter the harbour, the tide turns. Orcas' sensitive skin detects subtle changes in current, but they can get it wrong. Becoming stranded in the low tide is a very real risk for New Zealand orca. So they wait in the outer harbour and bide their time. Below them, lightweight animals are tossed about by the outgoing tide. Dislodged from its inshore home, this sea hare is way out of its depth. A primitive mollusk, it probably perceives the fierce current as a threat. So it uses the only defence it has, its ink. But it's the tide that is the driving force of this entire ecosystem. In every corner of the harbour, there are organisms adapted to survive and thrive in its rhythms. The outgoing tide rolls a tiny seed along the harbour floor. While most trees' seeds are dispersed by wind or animals and would perish in salt water, this remarkable pod relies on the tide to carry it. It's a compressed version of a fully formed tree. Packaged up in a flotation raft, complete with food supply. Everything it needs for a long sea journey. And this is what it will become. A mangrove. A subtropical tree that lives underwater. They are brilliantly adapted to their saline world. A waxy coat waterproofs their leaves. And their roots are shallow, but spread five times further than land trees' roots. They trap silt and stabilise soil that might otherwise be eroded by the tide. Mangroves provide habitats for other plants, like Neptune's necklace. Fish shelter among their branches. And barnacles cling to the wood. Their feathery fans filter plankton from the currents, feeding while they're breeding. The long tendril extending to the right of each of these individuals is a penis. Relative to body size, barnacles have the longest penises in the world. Mangroves and the creatures that live among them attract all sorts of birds. Kingfishers, herons and spoonbills. They wait in the upper reaches of the harbour for the feast the low tide will expose. While the wary orca keep to the deep. New Zealand has the world's highest incidence of orca strandings. And impatience could cost them their lives. The tide is on its way out in the Hokianga Harbour. The rays venture into the deeper water of the outer harbour. Even they can become stranded if they ignore the tide. For the orca, miscalculating the harbour's daily rhythms could cost them their lives. If one becomes beached, it endangers the entire pod, as these highly social animals do everything together. There are fewer than 200 known individuals in the whole of the New Zealand orca population. Around half of those frequent North Island waters. Calves are more than two metres long at birth and are never far from an adult. Females have a small curved dorsal fin. And an adult male is easily recognised by his much longer straighter fin. Although every one is unique. Some made more distinctive by injury. The fact that wounded individuals can survive long enough to heal highlights an extraordinary feature of orca life. In the animal kingdom, injured adults are usually left to perish. But orca populations are known to support wounded males, who, at least temporarily, cannot hunt. They also protect older females way past breeding age. Many even live through menopause, some well into their 90s. The only other mammals to do this are pilot whales and humans. One reason for this is that orca do everything cooperatively. Each member of this tightly knit pod has a job to do. From hunting to childcare. A calf nudges his mother's flanks, asking for milk. He will be dependent on her for the first two years of his life. Almost directly below them is another devoted mother. This large conch shell is a hideout for a female octopus. She chose it for the most important undertaking of her life. Laying her tiny white eggs. Tens of thousands of them are crammed into the shell around her head. As she prepared to lay, she gorged herself on crabs, shellfish and possibly even the conch, which once owned her shell. But from the moment she laid her eggs, hormones suppressed her appetite. And she stopped eating. In the coming months, she will do nothing except aerate, groom and guard her eggs. A passing male makes the mother change colour defensively. Octopuses are highly territorial, and they have astonishing powers of camouflage, changing colour at will. The mother in her hideout has passed this ability on to her young. And it's never too early to start practising. The debris of the mother's last meal has become her fortress. And it's also a great place for another shell-borrowing species to rummage for new material. Hermit crabs never stay long in their borrowed homes. In this case, whelk shells. Their bodies are soft and they have no shell of their own. So they appropriate others. As they grow, they just move into bigger shells. But this hermit crab has more sense than to expose its soft body right next to an octopus's den. So it drags its new house across a vast expanse of sand. Right into the path of the other octopus. They eat crab. But this one seems more interested in hiding than hunting. Orca eat octopus. Perhaps the octopus senses there are orca in the harbour. Among the shells in its hideout, a mangrove pod pauses on its way across the harbour. Rolled all the way here by the outgoing tide. The current eventually moves it on. It has a long way to go before it finds a suitable place to settle. But it's unfolding its roots in readiness. New Zealand is the southernmost place in the world where mangroves grow. And yet in Northland, there are 6,300 hectares of mangrove forests. Frost shy and thirsty, these strange and beautiful trees need calm water and a warm climate. They are happy underwater as long as it's only half of the time. Like all trees, they still need to breathe. The low tide reveals another brilliant adaptation to life in their watery world. Most trees gather oxygen from the soil. But mangrove's roots grow out, then up like snorkels. These breathing roots are the mangrove's lifeline. As the tide recedes, the barnacles that live on them close their shells to conserve moisture. And wait it out. All along the shoreline, it's a race to shut down before the water disappears. And take cover from the drying air. Mud crabs duck under rocks or into their holes. But an even grislier death awaits those who fail to disappear. Low tide is the time these hungry shorebirds come out to hunt. After a journey of many kilometres across the harbour, the mangrove seedling nears the shore. It will only have a few hours to establish itself in its new home. Or the next high tide will carry it away. But already its root system is starting to unfold. And all these seedlings show this is a good place to settle. For a few short hours between tides, the mangrove's breathing roots are exposed and they take their fill of oxygen. Mud snails hoover up the film of minute plant life called phytoplankton left by the outgoing tide. While crabs forage on the tiny creatures it has exposed. But with reward comes risk. Each bird in the neighbourhood has a different adaptation for foraging in the intertidal zone. A white-faced heron stalks with stealth and patience. Light and speedy kingfishers hunt in any environment that offers them an elevated lookout over water. But they have to break open the mud crab's shell. Although their prey is similar, each bird has a different zone to exploit at low tide. This little black shag has bitten off more than it can chew. An expert diver, the shag catches a large flounder from the harbour floor. But it's no use to the shag if it can't hold on to it. The spoonbill has organs inside its beak which detect vibrations of prey. So it can hunt by day or night. It's the level of the tide that matters. The water needs to be about as deep as the length of its bill, which it uses like a spoon to stir the shallows, dislodging insects, shellfish and small fish. Pied stilt's long legs are especially adapted for stepping through the shallows. While they, like the oyster catchers, probe for shellfish deep in the mud. But sometimes they get more than they bargained for. In some Northland harbours, shorebirds and their prey are locked into a cycle of parasite infestation. These cockles, with their fringed feeding tubes open, are filtering microscopic larvae from the sea. One variety is hatched from a parasitic worm that invades the guts of shorebirds. They excrete its eggs into the sea, which hatch into larvae, which are then eaten by the cockles. The cruel twist for the cockles is that the parasite constricts the muscle they would normally use to bury themselves, making them easier pickings. The birds eat the infected cockles, become infected themselves and the cycle repeats. At low tide, there is still water in the shallow channels that wind through the mangrove swamps. Here, small fish hide from bigger predators and wait for high tide. Just after midday, the tide turns. As it comes in, the fish go out, back to the outer harbour to feed. Caspian terns follow them to pick off stragglers. With the return of the tide, the barnacles reopen to catch fresh incoming plankton. But with the tide, come hunters. As soon as the shelly mudflats are underwater, the rays return to the inner harbour to feed. Like the spoonbills, rays don't see their food. They sense electric signals of their shellfish prey. With the turning tide, the orca have their cue at last, to move inshore to hunt. Orca the world over eat prey as big as whales and sharks and as small as fish and octopus. But the orca group that frequents the Northland harbours has developed a taste for a delicacy rarely eaten by orca anywhere else in the world. Rays. Every ray hunt involves dicing with death. One blow from a stingray's tail barb will cause a wound that fast tracks the ray's poison straight into the bloodstream. Orca have been known to die this way, so they must be coordinated, clever and cautious. Northland orca have refined techniques for hunting these dangerous delicacies. Strategies that are unique in the world. Every pod member has a part to play. An adult supervises the very young. Then there are the apprentices. This young female with her dorsal tip missing seems anxious to join in. But until the ray with its deadly weapon is disabled, she must hang back to watch and learn. While the pod's more experienced hunters launch a synchronised attack. Orca know that if a stingray is flipped onto its back, it enters a defenceless trance-like state. But getting hold of the wriggling ray without being whipped by that tail barb takes patience. This wily orca turns itself over to get the ray on its back. But it adjusts its grip and the prize is lost. This is the ray's chance to escape. But it's clearly disoriented. Sometimes orca are swift and businesslike with their prey. Other days they test the ray and pass it until they're satisfied its weakening. On its back at last, the ray is subdued. But it's still dangerous. So the male passes it to a waiting female who is perfectly positioned to inflict the death bite to the ray's head. Now it's finally safe to eat, she does an extraordinary thing. The adult actively offers the catch to the young apprentice to practice handling the now harmless prey. This adult is doing the same thing, sharing another ray with a juvenile female. Hunting is a team exercise and the spoils are almost always shared. Hands, orca cannot hold their sinewy prey to dismember it. So enlisting another individual to help tear it apart breaks the food into small portions and ensures everyone gets fed. Brutal though they seem, it's orca's hunting techniques that best illustrate their contradictory nature. These ferocious predators every act is performed in the interests of the group. But a single ray is not enough to sustain a hungry pod of several 7,000 kilogram mammals. The hunt continues. This time it's an eagle ray. Every bit is desirable. Every bit is dangerous. The commotion of the hunt, the element of surprise is gone and the orca must give chase. Flat as a pancake, the eagle ray can deftly navigate the shallows, the only place it has a chance. Shallow water is the orca's mortal enemy. If one beaches, the pod is doomed. The incoming tide transforms the Hokianga Harbour from a muddy bog to a lush water world. At last the fish can leave the channels and head out into the deeper harbour to find food and to avoid the larger hunters as they move further inshore. Fanworms filter feed on plankton with their feathery arms, reacting as goatfish swim over. These are a local variety, but an invasive Mediterranean species has infested some Northland harbours, competing with indigenous shellfish for food. Deep below them a little cardinal fish hovers and it's the last thing it ever does. Buried in the sand was a stargazer like this one. The stargazer's face is built upside down with the mouth uppermost on its head, making it a brilliant ambush predator. Whereas the flounder's face is all on one side. Another bizarre adaptation for life in a tidal environment. It can grow to over 22 centimetres from dorsal to pectoral fin and yet it can swim in only three centimetres of water. On its side, both eyes up. Flat like a flounder, the eagle ray seeks shelter in the shallows from the huge orca. Still hungry after their last catch, the pod, including the young half-finned apprentice, has chased the eagle ray dangerously close to shore. The ray is trapped and the orca simply help themselves. But they're in grave danger of beaching. Top priority is to get out to deeper water without being stung by the eagle ray's venomous tail barb. The ray does everything in its power to escape. It even tries to leap out of the water. But the canny orca recapture it and hurl it through the air. This technique has never been observed in any other orca population. They pass it underwater too, so one of the hunters can get a secure grip. But the intelligent orca won't attempt a catch if the tail is a risk and the ray escapes. But not for long. It's gravely injured, its wing shredded by the orca's razor-sharp teeth. Even a healthy eagle ray with a top speed of around 48 kilometres an hour can't possibly out-swim the orca. This ray has no chance. The young apprentice is as keen as ever to join the hunt. The team easily picks up the helpless animal and tears it open. Finally, when the ray is no threat to the orca, the adults hang back and allow the young female to hunt alone. She then does exactly what she's been trained to do. She takes the best part, the liver, and avoids the head and tail. But the ray is no danger to anyone now. And the adults go in search of their next target. Nothing goes to waste in the sea. Hundreds of little mouths wait until the coast is clear. All over the harbour floor, scavengers devour larger predators' scraps. Prey eat predators, feasting on animals that usually feast on them. The remains of the elegant ray are finally eaten by snapper. And even the tiny mollusks it used to prey upon. The determined hermit crab still drags its new shell across the sand. As far away as possible from the octopus's den. As the embryonic larvae grow stronger in their eggs, their devoted mother grows weaker. She has not eaten for months now. Soon her tiny young will hatch and her work will be complete. But so will her life. The floors of the Northland harbours bristle with young mangroves. Some seeds will have fallen straight from the trees above. Others will have survived epic journeys across the harbour, or even the ocean, to root themselves in the soft mud in the brief interval between tides. Between their breathing roots, the snails repossess their muddy playgrounds. Safe for a few hours from the birds above them. The herons and the spoonbills, squabbling over pole position while they wait for the next low tide. The rays remain watchful and defensive as they forage for shellfish on the harbour floor. Or pursue a mate, whether she is interested or not. Some bear the telltale scars of an orca encounter. Like this eagle ray with unmistakable orca tooth marks on both its wings. And possibly this female longtail. With no tail. The determined hermit crab finally decides it's safe to end its epic journey and slip into something more comfortable. This other shell. The trick is to position the shells to minimise the time that its soft body is exposed. Then the crab simply reverses into its prized new home. Every one of the hermit crabs living around the female octopus's hideout will have to move house like this. Perhaps a hundred times in their short lives. After months of their dedicated mother tending, aerating, grooming and guarding them. The tiny octopus eggs hatch. There are tens of thousands of them. In her final maternal act, she brushes them free. And blows them out into open water. Then there's nothing more their mother can do for them. As they are carried away from her by the tide. They become part of the planktonic mass that forms the basis of the harbour food chain. Fewer than 1% will survive to adulthood. Many won't even survive their first day. And neither will their mother. Like all common octopus females, she's only lived for two years and bred just once in that time. Males don't stay around. The female is left to guard and tend the eggs alone. So nature ensures she will not abandon her post by switching off her desire to eat. A peaceful passing is not assured. She'll not put up a fight. She's passed on her genes to the next generation. Her work is done. Above her, another family pass on more than their genes to their young. As the half-finned apprentice graduates to independent hunting, she will start to make a real contribution to her pod. Their hunting techniques, unique in the world, are learned, local and reinforced within the group. In the animal kingdom, this is the definition of culture. Fierce predators they may be, but orca are hunters with hearts of gold. As the sun sets over the mouth of the Hokianga Harbour, the orca's bellies are full, the tide is high and it's safe for them to rest. In a few hours, the outgoing tide will compel them to move on, perhaps to another of the Northland harbours. Perhaps further south, to another beautiful part of our big blue backyard.