When you've spent more than 10,000 hours swimming the world's oceans, you're bound to see some incredible sights. And if you're a talented photographer, you can bring those sights to people who may never witness the wonder of life under the surface of the sea.

Brian Skerry is one of National Geographic's most celebrated ocean photographers and has spent more than 30 years collecting images that explore the lives and challenges of marine species. One of the creatures that has most fascinated him over the years — and one that is currently most imperiled — is the shark. Skerry had his first encounter with a shark in 1982 and since then has been hooked, so to speak, on these perfectly evolved ocean predators.

At Tiger Beach in the Bahamas, tiger sharks have acclimated to the presence of humans (and know that many will have food for them). Vincent Canabal is an ecotourism guide who works at Tiger Beach and knows many of the sharks here on sight. At Tiger Beach in the Bahamas, tiger sharks have acclimated to the presence of humans (and know that many will have food for them). Vincent Canabal is an ecotourism guide who works at Tiger Beach and knows many of the sharks here on sight. (Photo: Brian Skerry/National Geographic)

An estimated 100 million sharks are killed in commercial fisheries every year, according to the Pew Charitable Trusts. The decline is due to the popularity of shark fin soup, overfishing and the capture of sharks as bycatch. As apex predators, sharks take a long time to reach reproductive age and don't reproduce very quickly, which means they can't replace themselves fast enough to counter how many are killed. Over half of all shark and ray species that have been assessed by the International Union for Conservation of Nature (IUCN) are classified as threatened or near threatened.

"I became a photographer because I love looking at pictures and because I am passionate about nature. Being able to combine these things means a great deal to me," Skerry told MNN in a past interview. "I also believe that photography is a very powerful tool and that it can make a tremendous difference. Humans are visual creatures and we respond emotionally to images. I believe that a single photograph can stay with someone for their lifetime."

This is never more apparent when it comes to showing the truth behind sharks, a species that frightens and fascinates us to an extraordinary degree and yet which most people really know quite little about. Powerful images bring to life the reality of these ocean predators and the plights they face for survival.

At Isla Holbox in the Gulf of Mexico, whale sharks gather to feed every year. From a boat it seems like these massive fish swim rather slowly, but when I got into the water, I was surprised by their speed. I wanted to swim ahead to capture the living wrea At Isla Holbox in the Gulf of Mexico, whale sharks gather to feed every year. From a boat it seems like these massive fish swim rather slowly, but when I got into the water, I was surprised by their speed. I wanted to swim ahead to capture the living wreath of scad circling this shark’s head, and just keeping up took a tremendous effort. (Photo: Brian Skerry/National Geographic)

Skerry has gone to amazing lengths to photograph shark species around the world in ways that illuminate how they live, their role in the ocean, and even who they are as individuals. Whether that is using decoys, swimming in or out of cages, and even hanging cameras from blimps, Skerry has gone far to create images that make viewers feel as if they are right there in the water with these incredible animals. And each image helps us get a little closer to understanding the mysteries of sharks.

"Although the lives of these animals remain enigmatic, there have been fascinating discoveries made by researchers, which along with the use of new photographic technologies make this a perfect and vital time for such stories," Skerry writes in National Geographic's PROOF blog.

Skerry's photographic work on these apex predators is collected in a new National Geographic book titled "Shark," which places 250 of his photos within chapters about the role sharks play in the ocean and the importance of conserving them, as well as fascinating, hair-raising and inspiring chapters on several species that captivate most people: great whites, tiger sharks, shortfin makos and oceanic whitetips.

Makos have a reputation as aggressive sharks, which is part ofbwhat makes people see them as such a prize catch. But these efficient, elegant predators are declining in number. Makos have a reputation as aggressive sharks, which is part of what makes people see them as such a prize catch. But these efficient, elegant predators are declining in number. (Photo: Brian Skerry/National Geographic)

The book reminds readers that saving sharks isn't simply about doing the right thing, it's also about doing something critical to the overall health of the sea. Without sharks, the apex predators that maintain the balance of marine ecosystems, our world's oceans take a severe hit. The stories are told with humor, emotion and respect, and partner beautifully with the photographs to provide a complete story.

Brian Skerry has spent countless hours with some of the most feared fish in the sea. Skerry has spent countless hours with some of the most feared fish in the sea, and the hard work has culminated in this beautiful book. (Photo: Brian Skerry/National Geographic)

Listen to Skerry talk about the ocean's beauty and conservation challenges, and you'll quickly understand the passion that went into the photographs behind his new book:

Jaymi Heimbuch ( @jaymiheimbuch ) focuses on wildlife conservation and animal news from her home base in San Francisco.