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.
“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.
“So we tested it, and not only did it work, but it was a swinging success,” says Kuguru, who is also a National Geographic Explorer and 2022 recipient of the National Geographic Wayfinder Award.
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.
“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.