The quicksilver ball quivered and seethed, mercury smoke flashing in the golden hour sunlight. I drew in breath and ducked below the surface, a few metres down hitting the icy layer of water driven up from the great depths. As I span onto my back I looked up to see the baitfish above me silhouetted against the sun, a living thing growing and receding before the dark torpedo shape of a predator. The large male California sealion darted amongst the fish trying to separate a loner, herding them like tiny silvery sheep. Out of the green a pod of clicking white-sided dolphins hove into view, bodies convulsing, vocalisations escalating in the excitement of the chase. I turn my camera skywards, battling the urge to breathe or surge for the surface hoping to capture this dazzling overwhelming spectacle, one you could spend a lifetime searching for.
It's a truth widely accepted in ecology that top of the line apex predators don't matter. That we're wasting our time putting effort into cuddly iconic carnivores, when the most important factors are always less charismatic but more abundant stuff like bugs and grubs. There is one place however where that has been proven manifestly untrue. That magical place is one of the world's greatest conservation success stories, and it's where I'll be spending my summer making Big Blue Live for BBC1.
It's a torrid tale with bleak beginnings, but a truly happy ending. California's Monterey Bay has been an epicentre for fisheries for 240 years, and as such has had every single one of its marine inhabitants brutally and fatally over-exploited. One of the first to be exterminated was the sea otters. As a marine mammal that is not insulated by blubber like whales and seals, sea otters possess the densest fur on the planet, 100,000 hairs per square centimeter.
It's an essential adaptation in waters that are blessed by cold upwellings of nutrient-rich waters; the very basis of the flourishing food chain. Their fur coats however proved to be their downfall, as waves of both legal and illicit hunters ravaged these shores in search of the priceless pelts. In the late 1700s they were seen as the royal fur in China, and in the 1800s a single pelt could raise $100. Not surprisingly the last sea otter disappeared from Monterrey before the end of that century. They were not the last to perish before human avarice. In 1854 a whale was worth two pounds of pure gold, and hence they too fell, first to spears then to the explosive harpoons of the industrial whalers.
Where once it was said you could walk across the bay on the backs of the plentiful whales, the business eventually collapsed as there were simply no whales left to catch. In the 1800s abalone brought the Chinese here. Seabird eggs were food for the prospectors of the Gold Rush, then from 1910-1940 the canning industry - immortalised by John Steinbeck's Cannery Row - became the biggest canned fishery in the world. Seals and sealions were clubbed out of existence, industrial pollution clogged the bay, and the waters were clogged with the guts of a billion sardines. Every single objective was targeted until it was functionally extinct, and then the humans would move on to something new.
But then the tide turned. Many give credit to one of the greatest unsung conservationists of all time. Julia Platt was the headstrong opinionated local who became the town's major (in the 1930s when such a thing was unheard of), and was the first to have the courage to take on the curmudgeonly might of the fisheries. She not only fought for regulation, but for complete no-take zones, and was part of a sea-change in attitudes, seeing environments and animals as having value above and beyond economics and tawdry lucre. The refuge outside the Hopkins Marine station still bares her name.
It's a philosophy that lives on today in Monterrey Bay Aquarium, to my mind the finest in the whole world, a centre for marine conservation of global importance, and our base for 'Big Blue Live'. Their vast exhibits of native kelp forests and deep sea environments swept with lavish shimmering shoals of sardines and tuna, are gazed at by 1.8million visitors a year. Yet intertwined with every jaw-dropping spectacle of aquatic wonder, is an accompanying exhibit of how such treasures are being destroyed, with practical advice of what we personally need to do to make a difference. Nobody could leave the aquarium without a sense of awe, but also of personal responsibility. It's a definitive counterpoint to the vile concrete pools of Seaworld, where proud dolphins and killer whales are taught to do cheap tricks for our pleasure.
But the real triumph of Monterey happened quietly sometime in 1938. Without fanfare, somewhere down the coast a sea otter returned. And then hundreds, and then thousands. Obviously this was a cause for celebration. Few animals inspire more cooing doe-eyed endearment to the general public (despite the fact that as the largest weasel, they are the size of an Alsation with teeth to match, and will occasionally kill the local harbor seals!). But what happened next, nobody could have predicted. Sea otters dive to the seabed, snatching up crabs, abalone and sea urchins, before bringing them to the surface and smashing them open on their stomachs - often with the aid of an anvil stone they keep stored under their armpit. When the sea otters were destroyed, their prey sources exploded, and devoured all the kelp. But sea otters have to eat a quarter of their substantial bulk every day.
When the sea otters returned, so did kelp forests that had not been seen in Monterrey for over a century. With urchin and abalone numbers kept in check, a whole environment bloomed. Composed of the fastest growing plant (strictly speaking an algae) on earth, these dense dark forest canopies are exactly like a submarine rainforest, green caves occasionally illuminated by fingers of God sunbeams that cut down into a bustling jungle beneath. The tendrils and wave-lashed wisps of weed are home to a bustling multitude, from tiny fish little more than plankton right up to giant pouty-mouthed bass. The forests became nurseries for the fish that were to restock the bay. Harbour seals and California sealions returned in their droves to feast on the bounty. Pelicans, gulls, sooty sheerwaters and cormorants returned in numbers that would be declared plague proportions... if there wasn't clearly enough food to feed them.
And then finally, the giants came back. Every day the team and I were out at sea in the bay we recorded vast shoals of baitfish, as well as a deeper layer of the crustacean krill that seemed everlasting. At night we dived amongst gargantuan shoals of market squid, here to spawn in their hundreds of tonnes. In one single day we recorded seven species of whale and dolphins, including the largest animals ever to grace our planet, mighty fin and blue whales. White-sided dolphins lunged and snorted in our bow wave as we raced along, curious melon-headed Risso's dolphin, their flanks scarred from battles with deep-sea squid, humpbacks that had journeyed across the vastness of the Pacific to feed the appetites of starving calves in the bounty of the bay. And this summer, we will be bringing this spectacle into your living rooms, as it happens, live. I hope that Major Julia Platt would have proud...
Big Blue Live continues on BBC One on Sunday 30 August at 7pm.