As the largest predatory fish on Earth, great white sharks are already impressive, armed with up to 300 serrated teeth and weighing up to 5,000 pounds. Now, new research adds more intrigue to the oceanic beasts, suggesting that the animals can change color—perhaps as a camouflage strategy to sneak up on prey.
In new experiments off South Africa, researchers dragged a seal decoy behind a boat to entice several sharks to leap out of the water near a specially designed color board with white, gray, and black panels. The team photographed the sharks each time they jumped, repeating the experiment throughout the day.
One shark, easily identifiable because of an abscess on its jaw, appeared as both dark gray and much lighter gray at different times of day. The scientists verified this using computer software to correct for variables such as weather, light levels, and camera settings.
The researchers then humanely extracted a small piece of tissue from one of the sharks and hurried it back to a lab, where they treated it with several different types of hormones naturally occurring in sharks.
Using a time-lapse camera and a confocal microscope, the researchers watched in awe as the great white’s melanocytes—skin cells that contain pigment—contracted and turned lighter in color when doused in adrenaline. At the same time, another hormone known as MSH, or melanocyte-stimulating hormone, caused the same cells to disperse, resulting in a darker skin color. (Read about a deep-sea shark that’s one of the biggest glowing animals on Earth.)
“We wanted to trick these shark cells into thinking they were getting some kind of stimulus, like the sun or an emotional stimulus [such as seeing potential prey] to see if we could get them to change and become lighter or darker,” says Gibbs Kuguru, a shark scientist at Wageningen University and Research in the Netherlands.
With data from a limited number of sharks, the scientists caution that the great white’s ability to alter its appearance is not yet validated, and that their research has not been published in a scientific journal. But other experts say the possibilities are tantalizing.
Unraveling secrets of the great white shark
Most of the focus on the great white in recent decades, understandably, has been on its charisma, says Ryan Johnson, a shark biologist at the Blue Wilderness Shark Research Unit in South Africa and Kuguru’s research partner.
“Their speed, their power, their size, their ability to overwhelm prey,” he says. “What excited me about this research was that we wanted to look into something incredibly subtle and microscopic.”
Anecdotally, Johnson and other scientists have noticed that great whites appear to alter the hue of their top half, or dorsal side.
This is different from countershading, which is a well-known camouflage strategy of many marine predators in which their top halves are naturally darker and their bottom halves are lighter. Countershading evolved to help predators remain inconspicuous from above and below by mimicking both the dark of the depths and the sunlight of the water’s surface.
But there’s nothing in the scientific literature suggesting that great whites can change color, which has motivated Johnson and Kuguru to keep studying the phenomenon. (Learn why great whites are still a mystery to us.
“Since we finished the program, we’ve been going out two to three times a week and just collecting hundreds of photographs of the sharks against the color boards,” says Johnson.
The hope is that by analyzing a larger data set, the scientists will not only be able to verify that the color change they have documented is more than a fluke, but also identify a pattern of when and why the animals go into camo-mode.
“A pretty exciting finding”
“From a publication standpoint, I don’t think anyone has tried to take on great white shark coloration like this,” says Michelle Jewell, who studies great white shark behavior at Michigan State University Museums and was not affiliated with the research.
“From personal experience, though, we definitely do notice changes in their color. But usually those changes have happened over a series of days.”
According to Jewell, the leading hypothesis for such changes is that the sharks were getting tans after spending more time in shallow water where the sun’s rays are stronger.
That’s not as silly as it sounds. A 1996 study showed that when captive juvenile scalloped hammerheads were corralled into shallow waters, they gradually became darker than did hammerheads allowed to dive into deeper waters.
“We didn’t consider that this could potentially be something that they themselves are manipulating to get darker or to get lighter,” says Jewell. “But it would make a lot of evolutionary sense.”
However, given how the extremely large animals can appear out of nowhere, even when water visibility is exceptional, it would make sense that great whites have evolved to enhance their countershading camouflage.
“It wouldn’t surprise me that they can do that just because of how freaking good they are at sneaking up on you,” says Probst, who has spent hundreds of hours in the water with more than 200 great whites. “They’re ambush predators that rely on stealth.” (See a video of a giant great white feeding on a sperm whale.)
Gregory Skomal, a shark expert and head of the Massachusetts Shark Research Program, says he, too, is not completely shocked by the preliminary research, though he’d like to see it backed up by a more structured scientific study.
“We know many species of fish are capable of changing their color tones,” says Skomal. “So I think it’s a pretty exciting finding."