Video shows rare whale sharks just 100 miles off New York City

It was a sight you'd expect to see in tropical waters, not off the coast of New York City.

Massive whale sharks were recently spotted surfacing right next to a boat, turning an ordinary day on the water into an extraordinary encounter.

For a moment on Monday, everyone on board stopped what they were doing as two whale sharks cruised through the water, just feet from the boat. And for Chris St. Lawrence, a naturalist for American Princess Cruises, it was the kind of rare sight you don't forget.

"Once in a lifetime, to say the least. You can hear the reactions in the video -- everyone freaking out," St. Lawrence said. "The water was just so clear. You can see everything. You could also see the spotted pattern on the shark, which is how scientists can tell them apart."

St. Lawrence was out on one of the company's special offshore trips, when the unexpected appeared about 100 miles off New York City near the massive submarine canyon known as Hudson Canyon.

People rushed from one end of the vessel to the other, trying to get a closer look.

"People aren't aware we have these amazing ecosystems right off the coast of New York," St. Lawrence said.

The excitement was written all over their faces. People were cheering, high-fiving and celebrating a moment they know they may never see again, since marine biologists say the global whale shark population has declined more than 50% over the last 75 years.

Experts say whale sharks are harmless to humans. They were placed on the endangered species list nearly 10 years ago.

"Something like a whale shark, as massive as they are, are filter feeders. They're just filtering small fish and shrimp," said marine biologist Joe Yaiullo, curator and co-founder of the Long Island Aquarium.

Yaiullo said the gulf stream can bring warmer water and plenty of food up north, creating conditions that can draw species like whale sharks closer to our shores.

"So maybe 50 years ago, it wasn't getting warm enough up here, but now that things are getting a lot more warmer, we will see range extensions of all kinds of animals," Yaiullo said.

But for St. Lawrence, there's still something magical about not knowing what might be waiting beneath the surface.

"It makes you want to go back out there and keep looking for whatever else you can find," St. Lawrence said.