Mysterious Creatures Of The North Atlantic Ocean | 4K UHD | BBC Earth

Holding my breath, I free dive to the action. One whale swims under a shoal of sprat, which drives the fish up to the surface. Common dolphins have also found this shoal, but the minkes are the dominant force here. I keep my distance so as not to interfere. The minkes sometimes blow a short line of bubbles near the shoal of sprat. I've never seen this behaviour before. It seems the whales could be using the bubbles to partly herd the sprat. After half an hour, it's all over. The birds take off, perhaps searching for more shoals. You can actually smell the fertile areas in the ocean, because phytoplankton give off a gas known as dimethyl sulfide, DMS, and seabirds have an incredible sense of smell. And I wonder if they use that to find the fertile areas in the ocean and the shoals of fish. Maybe even whales and other animals could follow concentrated flocks of seabirds feeding. There's so much that we don't know still. But when you think, you know, a shoal of fish might be 20 metres wide in an area of the ocean, it could be tens of thousands of square kilometres. It's quite a feat for these animals to find them. So maybe the sense of smell is what's driving the whole thing. But what a wonderful scene. Thousands of seabirds, common dolphins and more than a dozen minke whales, all feeding on shoals of sprat and sand eel, who themselves are here to feed on the plankton. For thousands of years, shoals of herring had gathered in the small bays of our North Atlantic coast. For several winters now, I've been trying unsuccessfully to find shoals of herring in our inshore waters. December is the key month when shoals would aggregate in these protected bays before spawning. And also when they were fished. The cold water at this time of year helps with spawning. The further north we go, the colder and darker it gets. But this can lead to more fertile waters. In the fishing port of Killiebeg's County Donegal, I go to sea like many a man before in search of these herring shoals. I'm using scuba as herring usually stay deeper. And these are cold, dark waters. At 20 metres depth, it's more or less dark looking down. After a few days effort, I sense movement and look towards the sun. Thousands of them. They scatter from my dive bubbles and seem to move in sync. They never allow me to get close. It's wonderful to find some herring after several winters of trying. But what a fabulous fish they are. The old folk called them the king of fishes. But they were also hugely important for the ocean ecosystem. Because herring feed on plankton and fish larvae and effectively convert that energy into the rich fatty fish that they become. But I have to wonder what these bays looked like maybe 100 years ago when the herring shoals were reputed to be, you know, two kilometres long. And what the wider ocean looked like at that time compared to now. The whales can sense the presence of the herring and dive in pursuit. Holding my breath, I dive to film the action. They're not easy to find in the darkness. Tiny bubbles rise from the deep like a gas. Then I see a cloud of them and a coast like. A massive shoal of fish emerge from the deep. Thousands and thousands of herring. Killer whales have found them and driven them up from the deep. With their sudden change of pressure, gas has burst from their swim bladders which control their buoyancy. The whales work together to squeeze the fish into an even tighter ball. Gulls have spotted the signs. The killer whales push the herring up, but the humpbacks will be there to profit from this. The whales flick their tails into the herring shoal to stun the fish. The animals briefly surface only to catch breath. Birds have learned to be in the right place. But then the humpbacks, with their enormous mouths and cooperation, take the lion's share. And after less than 30 minutes, it's all over and the animals leave to search for more herring shoals. It's my chance to document these animals. It would be my first time in years of trying to film a fin whale underwater. Being in the water with whales this size is something I've learned to do safely over many years now. But it's still scary. I think about my ancestors and wonder what they would have made of this. The fin whale swallows an enormous mouthful of sprat and dives, coming within a few short meters of me. An awesome animal. Water visibility is just a few meters. What an incredible moment. To my knowledge, it's the first time anyone has filmed a fin whale underwater in Ireland. And then a humpback whale. But this is no ordinary humpback whale. I can recognize from the tail and dorsal fins that this is Boomerang. A whale that has been coming to our south coast for 20 years now and for some reason always associates with fin whales. He blows a single line of bubbles, perhaps to herd the sprat, and lunges from below the water. Humpback whales usually blow circles of bubbles to entrap fish. But this animal is just blowing a line. Perhaps he's competing with the fin whales. Again and again they rise, one giant mouth after another. Four fin whales feeding. Oh my god, they're 20 meters and up to 80 tons weight. That's two fully loaded articulated trucks for 16 elephants. On St Brendan's voyage, the monks wrote of having arrived at a coagulated sea. A place where the water appeared oily and absolutely no wind. All they could do was wait. I go for a swim in clear blue water. Salps are a chain of creatures living together. They suck sea water through their bodies to filter plankton. And this also propels them forwards. A mother and very small calf. This doesn't feel like Ireland. We're here finally, on the edge of the continental shelf, 250 kilometers southwest of Ireland. This place is called the Porcupine Seabight. What's incredible about here is that the seabed, as you come west of Ireland, it's about 200 meters deep. And then suddenly it just drops down to 1,000 meters, then 2,000 meters, and then eventually to 5,000 meters, the abyssal plain. That's more than half the height of Mount Everest. And you can see the conditions are just, I mean, it's surreal. It's absolutely beautiful here. And the water, it's blue, crystal clear and blue. Not like the coastal waters we get in Ireland, which are green because there's so much organic matter and plankton in there. Here, it's blue and we can see for maybe 15 meters. What we're hoping to find here is the fin whale. We've managed to film them in the inshore waters close to Ireland and other parts of the North Atlantic. If we can find them here and maybe film or photograph the back of their heads, the chevron and the blaze pattern that's unique to every individual fin whale, a bit like our fingerprints are to us, then maybe we can confirm some migration routes of these animals or at the very least show the different areas where they're feeding and they're moving around and try to protect them in all those areas and the areas in between. Right here on the edge of the continental shelf to the west of Ireland, it's one of the most fertile places in all of the North Atlantic, and this is where they're likely to be. I've ventured here to the Mid-Atlantic Ridge in search of fin whales. I believe they may come here to feed. These underwater mountains are known as seamounts and they can be hugely fertile areas. Because of their shape in the middle of the ocean, they cause nutrient-rich water to well up from the deep, creating oases of life in the open ocean. In places, they rise within a few metres of the surface. In other areas, they may peak at 40 or 50 metres deep. I dive in a seamount almost 100 kilometres from any land. Shoals of barracuda gather here to feed on smaller fish, as do these triggerfish. They even try a bite of me. Shoals of small snipefish gather in numbers and squeeze together to form bait balls. The larger triggerfish, barracuda and other smaller fish arrive to feed on this open ocean bounty. Blue sharks migrate here annually because they know there'll be fish. In the relative barrenness of the open ocean, the seamounts of the Mid-Atlantic Ridge are an oasis of life for sea creatures. It's funny, the sea can be so much more stable at depth than it is at the surface. West of the clear coast, some ocean giants have arrived. I wonder what St Brendan and the early seafarers in their open boats would have made of these creatures. Basking sharks. I can only imagine how many sharks they would have encountered in the Atlantic waters a thousand years ago. Did the sharks terrify them? Or did they perhaps spend time getting a sense of the animals and their quiet nature? We see basking sharks for maybe a week or two every year in sunlit spring waters. When they arrive to feed on plankton. And then just sporadically over the summer. They then disappear in early autumn for another eight months. Where do they go? We're really not sure. There are almost no winter sightings of basking sharks in our inshore waters. They appear to be gentle giants. But we really only see them when they're feeding on plankton at the water's surface. Gliding gently to catch as much plankton as they can. Filtering it from the seawater with their gill rakers. But I'm not convinced they're just docile creatures. At up to 10 metres and 5 tonnes, these are intimidating animals to meet in the open ocean. In sunny Atlantic waters, 30 kilometres south of Ireland, I'm searching for open ocean sharks. Sadly, most all of the 40 species of sharks in Irish waters are now in trouble. Unlike basking sharks, most others are predatory sharks. That is, they have teeth and strong jaws to eat fish. They're curious animals. Blue sharks are the most common predatory shark in Irish waters. They're highly evolved hunters in their own ocean environment. The pores around their heads are sensors filled with gel that can sense the tiniest movement of fish or other prey. And humans are of no interest to these animals. They migrate all around the North Atlantic, visiting Ireland in the summer months to feed, then travelling to these oars and America. In the last decade, however, their numbers have dramatically fallen because of chronic overfishing. These blue sharks have more than likely circumnavigated the North Atlantic. They migrate with the seasons, I guess. You could say they live by the seasons. And they come into Irish waters in mid to late summer when the water warms up a bit to feed, I guess. You know, sharks have been around for 400 million years. There was a shark fossil found in the burn dated to 300 million years ago. But what I find incredible is that about 100 million years ago, most shark species actually stopped evolving because more than likely they'd reached the perfect form to hunt and to live and survive in the ocean. They've likely come into our bays and our shallow waters for hundreds, if not thousands of years. And I can find no credible record of a shark attacking anybody in Ireland or any place close. But I'm really curious. They come right up to the camera. What a privilege to share the water with these creatures. Look at these absolutely beautiful animals. Ocean creatures migrate. Some to wherever the winds and currents bring them. Others quite deliberately to where there is food and they can breed. And sometimes feed on other animals. To the elemental beauty of jellyfish, we're seeing increasing numbers of them in recent years, possibly due to a decline in predators who hunt them like turtles. They abound in our summer waters, drawn to the life-giving energy of the sun. Barrel jellyfish are the largest in our waters. They can provide shelter for juvenile fish. And because of this, scientists now believe that the increase in the number of jellyfish may actually help fish stocks. Jellyfish are inescapably drawn to the sun. Living for just a few months, they strive to reach maturity, chasing the bounty of the early summer plankton bloom. Like most creatures, they appear to have two life goals. To reach maturity and reproduce. I dive with this beautiful shoal of compass jellyfish in our warm summer waters. They've come together to breed.