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Off the western coast of Mexico's Baja California, Guadalupe Island (map) is a shark mecca, drawing people from around the world hoping to catch a glimpse of one of these majestic creatures.

Divers recently exploring the area weren't disappointed.

Biologist Mauricio Hoyos Padilla posted a Facebook video of what he claims is the biggest great white shark ever filmed: An approximately 20-foot (6-meter) long female dubbed Deep Blue.

According to the California Department of Fish and Game , great white sharks can grow up to 21 feet (6 meters) long.

However, most great whites are around 12 to 14 feet (3.6 to 4 meters) long, says Christopher Lowe , a shark biologist at California State University in Long Beach. A 17.9-foot-long (5.5-meter-long) male great white was caught off Guadalupe in fall 2009. (Related: " Biggest Great White Shark Caught, Released .")

Deep Blue is "clearly a very large shark," he says.

There may be another reason for that: Instead of the slim, torpedo shape of most white sharks, "she's pretty rotund," adds Lowe. "Just by the looks of her, I'd say that she's pregnant."

Hope for Sharks?

As waterproof video cameras become more popular, people are increasingly filming these massive beasts—and expanding scientists' views on the upper limit for white shark size.

"That's the thing that changed the game these days," says Lowe.

At the same time, numbers of white sharks—the largest predatory fish—have dropped precipitously in recent decades due to overfishing for their fins and teeth and getting caught in fishing nets. The International Union for Conservation of Nature lists them as vulnerable to extinction .

One exception is the U.S.— two new studies say that the iconic species is doing better than expected off the East and West Coasts of the U.S .

The overall drop in population means that many white sharks don't get old enough to reach huge sizes, like Deep Blue.

Hoyos Padilla, director of Pelagios Kakunjá, a nonprofit supporting migratory marine species of the Mexican Pacific, estimates Deep Blue is roughly 50 years old. (Also see " Scientists Track a Great White Shark Across the Atlantic for the First Time .")

"When I saw Deep Blue for the first time, there was just one thought in my mind: Hope," Hoyos Padilla wrote on Facebook.

Dispelling Shark Myths

That's because Hoya Padilla—as well as Lowe—believe that Deep Blue's video, as well as more knowledge of sharks, can help dispel some of their myths.

For one, the majority of white sharks won't immediately swim up and attack you, says Lowe: The video captures Deep Blue nonchalantly gliding next to the diver on top of the cage. (Also see " Great White Sharks Surround Paddleboarders in California .")

At the same time, it is important that people respect them as top predators of the sea. "It's not Disneyland," says Lowe.

There's also debate about the merits of public cage diving , which is depicted in the new video, he explains.

Though it does increase awareness of sharks, there's a risk that the fish either rely on the bait from the divers as a food source, or that they start associating—and seeking out—people with food.

Even so, says Lowe, "the more the public sees [about sharks], the better."