The Depths of the North Sea: Life in the Cold Abyss | Secrets of the Seas Ep. 1 | 4K UHD Documentary

The sea and its unique inhabitants. You don't always have to travel to exotic countries. Many miracles happen in unexpected locations. Tiny dramas, magnificent spectacles. The North Sea and the Baltic as we have never seen them before. The North Sea lies between the coast of Great Britain and mainland Europe. Many of its residents face their greatest challenges at the beginning of their lives. Stavanger. Here lives a hunter found almost everywhere in the North Sea. The small spotted cat shark. Fully grown they reach a meter long and have hardly any enemies. Neither in the depths of the fjord nor here close to the shore. It's mainly females that are seen here and with good reason. They lay their egg capsules in the shallows. The cord-like extensions give a good grip. Depending on the water temperature the embryos need between 5 and 11 months to mature. This cat shark baby knows nothing of its future. In fact it's born into the ideal environment. The vegetation offers perfect cover and plenty of prey. And yet unlike the adults these baby sharks are not at the top of the food chain. This neighbor in particular is a deadly threat. The anglerfish. An ambush hunter that relies entirely on its camouflage. Anglerfish can only catch prey that swim directly above them. Often days or weeks pass between catches. Only a few creatures can disturb an anglerfish. A brown crab looking for a shelter. It's not choosy. The anglerfish is annoyed. It has to find a new point of ambush. That's quickly done. The move was worth it. This catch will sustain him for days. Months later the egg capsules are empty. Time for the 10 centimeter long cat shark baby to explore Luzafjord. The newcomer is appraised by everyone. The wrasse are particularly fascinated by the little shark. But not everyone wishes him well. A hungry anglerfish. And it's not alone. They're lurking almost everywhere. every day. Only a few cat sharks survive their early years. Not even scientists could explain why the anglerfish spits the baby out again. But this little one gets another chance. Cat sharks aren't only at home in the Norwegian fjords. They can be found in the English Channel too. The southern entrance to the North Sea. For example here off the coast of northern France. This is the Pointe du Hoc in Normandy. Anglerfish are no danger in these waters. But cat sharks have another problem here. Though you wouldn't know it from these steep cliffs, the seabed is mainly sandy. Rocky oases like this are rare. Hidden beneath the rocks? Cat sharks. Not just one, but several. These little sharks are loners. But the shortage of suitable shelter makes them share. They hunt at night and sleep in the daytime in the shelter of the rocks. Cat sharks are not the only ones that have trouble finding a place that offers peace and security. Some really tiny creatures have a similar problem. One of them recently disappeared from coasts from France all the way to Denmark. Seahorses. This female is a real pioneer. As a larva she was brought here by the current. And she was one of the first to recolonize the gateway to the North Sea. It won't be easy for these creatures to reclaim the coasts further east. Seahorses can only make headway in seagrass that gives protection from the current. For a successful comeback one thing is needed. More seahorses. For weeks the female has been searching for a male. Her chances don't look good. The remaining seahorses live in seagrass clumps far from one another. The bare stretches between the oases are insurmountable for these poor swimmers. Once seagrass grew everywhere but fungus and pollution plagued it for decades. Today conditions are better and the seagrass might recover. But now what's left of the seagrass is being overwhelmed by a foreign seaweed. Japanese wireweed. Low tide at Pointe du Hoc. These shallows are completely covered by the wireweed. It's an extremely invasive species. Indigenous plants like seagrass are being progressively displaced. But seahorses benefit from the invasion. In some places the wireweed is already linking their seagrass oases. The seahorses don't care what they hold on to. Perhaps that's how this male got here. Our pioneer female waited weeks for a partner. Now she has her chance. She's done it. The mating dance begins. Now they're a couple. Maybe one day their offspring will colonize the coasts of the North Sea. Japanese wireweed is already waiting everywhere for them. So in the future seahorses could be at home in the Netherlands and in Germany once more. The North Sea is half as big again as Germany. And averaging less than a hundred meters deep it's a fairly shallow sea. But it's certainly not a calm sea. Winter storms rage, smashing against the cliffs of a lonely rocky island. Only when the wind dies down is the island seen in another light. Heligoland. In November every year its offshore dunes are a nursery for one of the North Sea's biggest predators. The grey seal. Like many females this one has given birth in the last few days. It's a boy. His mother belongs to the harem of a mighty male. Nearly three meters long and weighing over 300 kilos he is the undisputed ruler of the beach. His harem consists of about 10 females. He's patient. Only when they have weaned their young will the females be ready to mate with him again. And that's the goal of many other males too. A handful of adolescents are constantly trying to approach his females. If they can't keep the young bull away the boss turns up. For the younger males his appearance alone is enough. The beach master celebrates his dominance with a victory roll. He can be sure his females are watching closely. After all they only want to mate with the strongest partner. A few days later his son is taken to the sea by its mother. Initiation to the sea usually starts in the second or third week after birth. A baby grey seal stays with its mother for a month at most. Then it's on its own. The baby can't stay in the cold water for long. On land it's light colored fur is perfect insulation but it's not waterproof. This will only change at four weeks after the molt. Soon his mother will have other duties. Mating season is coming. Another female in the harem has sensed this too and some males have raging hormones. The beach master can't accept that. This adolescent tries to force himself on the female. The boss comes to her aid. The rivals are well matched. The beach master switches tactics using his enormous weight. The rescued female witnesses his commitment to his harem. He often fights to exhaustion. Their victory roll shows everyone he recognizes. While the challengers have only him as their opponent he has to take on several of them every day. This visibly weakens him. The baby is alone for the first time. Where is his mother? In fact she's only gone down to the water for a while to cool off but the little one doesn't know that. He looks for her desperately and is rejected everywhere. Seal mothers only look after their own young. His search continues. His father has a problem too. His strongest rival is challenging him again. The heavyweights are exhausted and yet they both sense things must be decided. The females are watching closely. Will the beach master stay ruler of his harem or must he abdicate? His rival retreats for good. The old man has his reward. A bull's dominance is usually short-lived. After two or three years it's over. In the meantime his son has found its mother again. In just a few days she will finally leave him to mate with the beach master once more. Perhaps one day this pup will rule over his own stretch of beach. For the moment he and his mother can enjoy their time together. For these giants to survive in the North Sea they need vast amounts of food. Often it's the smallest inhabitants that make this possible. Every year in spring tiny creatures gather in such masses they can even be seen from space. The North Sea becomes an abstract work of art. A work of art made of microscopic algae. Once the sun is strong enough in early summer they bloom and multiply in their billions. Hundreds of species of tiny crabs, jellyfish and fish larvae feed on them. Different kinds of plankton and they attract the North Sea's very largest resident. The basking shark. To 12 meters long weighing five tons. A real giant and yet the basking shark feeds exclusively on microorganisms. It has to filter up to 2,000 tons of water an hour. The contents of an Olympic swimming pool. Its meter wide mouth and special filter organs in front of its gills help it do this. Researchers suspect that these huge fish use their keen sense of smell to find plankton in the vastness of the sea. So a basking shark is rarely on its own for too long. Hardly anything is known about these largest inhabitants of the North Sea. They can usually only be observed when feeding. Their ballet is short-lived. As soon as the plankton clouds are gone the sharks move on. In the endless blue even these giants seem tiny. Finding food in the open sea is extremely difficult. So most of the biggest North Sea species hunt near the coasts. Around the Shetland Islands for example. These rocky shores are mostly bare but under the water it's a different story. Brown algae grow here. In these perfect conditions they form entire forests. Nurseries for countless sea creatures. The rulers of the kelp forest are the grey seals. The brown algae provide food and cover. it rarely hunts during the day. That piques the interest of the female seal. It would be easy to eat the octopus but her instinct to play takes over. Suddenly a strange clicking sound. A sound that will make any seal freeze. Orcas. They use the clicks to seek out prey. It's not just their size that makes them feared hunters but above all their intelligence and many different strategies. While the matriarch scours the shore with her offspring one of the males has positioned himself further out. If his family succeed in driving a seal towards him it'll have no chance. Second try. Then as if at a secret signal they end the hunt. The bull is no longer in hunting mode either. But why? He has knocked a seal unconscious. Now he's waiting for his family. The kill is shared. Everyone gets something. Normally these orcas hunt herring in Iceland but the pod keeps coming to the Shetland Islands. They're probably attracted to the kelp forest's rich food supply in the summer. It ended well for the female this time but there will be more attacks. While giants are free to roam the North Sea tiny creatures are often tied to one place. They have to deal with extreme conditions especially in the largest mudflats on earth the Wadden Sea. No habitat in the North Sea changes so fast is so dynamic for it is made of sand. Over the years a transformation becomes visible. It's not only long-term changes that affect life here but above all the daily ones. In contrast to other North Sea coasts the shore here descends very gradually. So everything is subject to the rhythm of the tides. Every few hours what was land is covered by water. One animal has adapted especially well to this. The shore crab. This male is looking for food. A dead whelk washed up with the tide. To survive in the Wadden Sea you have to seize every opportunity. Small shrimps, mussels or simple scraps he'll take anything. It's not just crabs that find food here. Enter the nomads of the air. Hundreds of thousands of migratory birds are here to eat their fill before continuing on to their breeding grounds. They're actually no danger to the male shore crab and yet it has to watch out now because its worst enemy is hiding among the birds. Eider ducks they mainly eat mussels and starfish but if they find a crab that's a special delicacy. For this male and the other crabs a deadly game of hide and seek ensues. If you don't take cover now you're easy prey. Once the legs are removed the rest is swallowed whole. The male shore crab was lucky. Everyone gets their share in the Wadden Sea but why is this habitat so overabundant? It's all down to the moon. Its gravitational pull drags the water of our seas towards it. That's why we have tides. This interplay constantly flushes fresh nutrients into the Wadden Sea. A paradise for lugworms. They sift the ground for food and then excrete it as sand. The worms, clams and crabs hidden under the surface not only attract masses of birds but plenty of other residents too. 2,500 species live in these waters. Most must either move back and forth with the tides or burrow down so they're always covered by water. Shore crabs don't have to. They've developed an ingenious trick. Even though they have gills they can survive out of water for a very long time. They use their mouthparts to create a stream of air supplying their gills with oxygen. It's summer. The migratory birds have long since flown north to raise their chicks. The male shore crab also wants offspring. He's looking for a mate and he doesn't have to search too far. This is his chance. Crab lovemaking is a little complicated. After all, both are armor plated. The male has to turn the chosen one round and slide her under his own body. It won't work out without her help. Suddenly she rejects him. A rival. He wants to mate with her too but there's only room for one here. His opponent retreats. A little later the male finds the chosen one again. They pick up where they left off. The North Sea mudflats are the largest of their kind on our planet. At first glance they look barren and empty and yet they feed millions of birds and provide a home for fish and small animals. A habitat of superlatives. The North Sea is certainly a sea of contrasts. From the depths of the fjords to the broad expanses of the Wadden Sea. The challenges for its inhabitants are as varied as the seascapes. Only those that overcome them will have a chance. Whether they're huge or tiny.