As a kid, I used to dream about the ocean. It was this wild place full of color and life, home to these alien-looking, fantastical creatures. I pictured big sharks ruling the food chain and saw graceful sea turtles dancing across coral reefs. As a marine biologist turned photographer, I've spent most of my career looking for places as magical as those I used to dream about when I was little. As you can see, I began exploring bodies of water at a fairly young age. But the first time I truly went underwater, I was about 10 years old. And I can still vividly remember furiously finning to reach this old, encrusted cannon on a shallow coral reef. And when I finally managed to grab hold of it, I looked up, and I was instantly surrounded by fish in all colors of the rainbow. That was the day I fell in love with the ocean. Thomas Peschak Conservation Photographer In my 40 years on this planet, I've had the great privilege to explore some of its most incredible seascapes for National Geographic Magazine and the Save Our Seas Foundation. I've photographed everything from really, really big sharks to dainty ones that fit in the palm of your hand. I've smelled the fishy, fishy breath of humpback whales feeding just feet away from me in the cold seas off Canada's Great Bear Rainforest. And I've been privy to the mating rituals of green sea turtles in the Mozambique Channel. Everyone on this planet affects and is affected by the ocean. And the pristine seas I used to dream of as a child are becoming harder and harder to find. They are becoming more compressed and more threatened. As we humans continue to maintain our role as the leading predator on earth, I've witnessed and photographed many of these ripple effects firsthand. For a long time, I thought I had to shock my audience out of their indifference with disturbing images. And while this approach has merits, I have come full circle. I believe that the best way for me to effect change is to sell love. I guess I'm a matchmaker of sorts and as a photographer, I have the rare opportunity to reveal animals and entire ecosystems that lie hidden beneath the ocean's surface. You can't love something and become a champion for it if you don't know it exists. Uncovering this -- that is the power of conservation photography. (Music) I've visited hundreds of marine locations, but there are a handful of seascapes that have touched me incredibly deeply. The first time I experienced that kind of high was about 10 years ago, off South Africa's rugged, wild coast. And every June and July, enormous shoals of sardines travel northwards in a mass migration we call the Sardine Run. And boy, do those fish have good reason to run. In hot pursuit are hoards of hungry and agile predators. Common dolphins hunt together and they can separate some of the sardines from the main shoal and they create bait balls. They drive and trap the fish upward against the ocean surface and then they rush in to dine on this pulsating and movable feast. Close behind are sharks. Now, most people believe that sharks and dolphins are these mortal enemies, but during the Sardine Run, they actually coexist. In fact, dolphins actually help sharks feed more effectively. Without dolphins, the bait balls are more dispersed and sharks often end up with what I call a sardine donut, or a mouth full of water. Now, while I've had a few spicy moments with sharks on the sardine run, I know they don't see me as prey. However, I get bumped and tail-slapped just like any other guest at this rowdy, rowdy banquet. From the shores of Africa we travel east, across the vastness that is the Indian Ocean to the Maldives, an archipelago of coral islands. And during the stormy southwest monsoon, manta rays from all across the archipelago travel to a tiny speck in Baa Atoll called Hanifaru. Armies of crustaceans, most no bigger than the size of your pupils, are the mainstay of the manta ray's diet. When plankton concentrations become patchy, manta rays feed alone and they somersault themselves backwards again and again, very much like a puppy chasing its own tail. (Music) However, when plankton densities increase, the mantas line up head-to-tail to form these long feeding chains, and any tasty morsel that escapes the first or second manta in line is surely to be gobbled up by the next or the one after. As plankton levels peak in the bay, the mantas swim closer and closer together in a unique behavior we call cyclone feeding. And as they swirl in tight formation, this multi-step column of mantas creates its own vortex, sucking in and delivering the plankton right into the mantas' cavernous mouths. The experience of diving amongst such masses of hundreds of rays is truly unforgettable. (Music) When I first photographed Hanifaru, the site enjoyed no protection and was threatened by development. And working with NGOs like the Manta Trust, my images eventually helped Hanifaru become a marine-protected area. Now, fisherman from neighboring islands, they once hunted these manta rays to make traditional drums from their skins. Today, they are the most ardent conservation champions and manta rays earn the Maldivian economy in excess of 8 million dollars every single year. I have always wanted to travel back in time to an era where maps were mostly blank or they read, "There be dragons." And today, the closest I've come is visiting remote atolls in the western Indian Ocean. Far, far away from shipping lanes and fishing fleets, diving into these waters is a poignant reminder of what our oceans once looked like. Very few people have heard of Bassas da India, a tiny speck of coral in the Mozambique Channel. Its reef forms a protective outer barrier and the inner lagoon is a nursery ground for Galapagos sharks. These sharks are anything but shy, even during the day. I had a bit of a hunch that they'd be even bolder and more abundant at night. (Music) Never before have I encountered so many sharks on a single coral outcrop. Capturing and sharing moments like this -- that reminds me why I chose my path. Earlier this year, I was on assignment for National Geographic Magazine in Baja California. And about halfway down the peninsula on the Pacific side lies San Ignacio Lagoon, a critical calving ground for gray whales. For 100 years, this coast was the scene of a wholesale slaughter, where more than 20,000 gray whales were killed, leaving only a few hundred survivors. Today the descendents of these same whales nudge their youngsters to the surface to play and even interact with us. (Music) This species truly has made a remarkable comeback. Now, on the other side of the peninsula lies Cabo Pulmo, a sleepy fishing village. Decades of overfishing had brought them close to collapse. In 1995, local fisherman convinced the authorities to proclaim their waters a marine reserve. But what happened next was nothing short of miraculous. In 2005, after only a single decade of protection, scientists measured the largest recovery of fish ever recorded. But don't take my word for it -- come with me. On a single breath, swim with me in deep, into one of the largest and densest schools of fish I have ever encountered. (Music) We all have the ability to be creators of hope. And through my photography, I want to pass on the message that it is not too late for our oceans. And particularly, I want to focus on nature's resilience in the face of 7.3 billion people. My hope is that in the future, I will have to search much, much harder to make photographs like this, while creating images that showcase our respectful coexistence with the ocean. Those will hopefully become an everyday occurrence for me. To thrive and survive in my profession, you really have to be a hopeless optimist. And I always operate on the assumption that the next great picture that will effect change is right around the corner, behind the next coral head, inside the next lagoon or possibly, in the one after it. (Music)