This year marks the 10th anniversary of National Geographic’s Sharkfest, and NatGeo is commemorating the occasion with an intriguing new documentary exploring whether great white sharks can change their color to hunt more effectively. Camo Sharks follows marine biologist and research coordinator for the Blue Wilderness Research Unit Ryan Johnson and graduate student Gibbs Kuguru in the field as they attempt to gather evidence to support the hypothesis that these ocean predators can enhance the dermal cells in their skin to change color as masking agents.
A native of New Zealand, Johnson grew up in a beach town where he absorbed the conventional wisdom that dolphins were “the good guys” and sharks were “the bad guys.” When he decided to become a marine biologist, he wanted to work with dolphins. When he was in his 20s, he had the opportunity to do some research on great white sharks in South Africa, which at the time was facing massive pressure from overfishing, leading to an increase in shark attacks.
“They’ve just become very popular as a delicacy,” Johnson told Ars. “The shark fin soup business went crazy, and [sharks] were being killed en masse. It was a wake-up call for me. I realized that it needed attention, at least from my point of view, a lot more, compared to dolphins.”
Since then, Johnson has studied such questions as whether the white shark cage diving industry is making sharks increasingly dangerous to humans and has conducted satellite and acoustic tracking of great whites. He has also studied the impact of ecotourism on sharks, researched the bite force of great whites, and studied predator-prey games between great whites and the seals they hunt.
Based on his experience in the field, Johnson had long thought that great white sharks might be able to change their color. Shark scientists identify specific animals by their dorsal fins, scars, and other distinguishing features. He recalled that he and his team would often see a light-colored shark in the morning and another darker-colored shark in the afternoon, assuming they were two different animals. “But then you’d go back and look at the photos and think, ‘Oh, this isn’t a new shark. This is the same one. The dorsal fin markings are the same,'” Johnson said.
Then he met Gibbs Kuguru, doing his Ph.D. work on color changes in blacktip sharks in the Maldives. “I said, ‘Hey, man, what if I told you that even great whites change color?'” Johnson recalled. Kanguru thought the idea sounded fascinating, and the pair began researching the subject. For example, they found cases of hammerhead sharks sunbathing and certain rays that could change their color.
Other past studies have found that zebra sharks change color as they age, and rainbow sharks can sometimes lose color due to stress and aging. And as we reported in 2019, a new family of small-molecule metabolites in the lighter parts of the skin of swell sharks (Cephaloscyllium centrism) and chain sharks (Scyliorhinus retifer) allows them to absorb blue light in the ocean and essentially turn pale green, so they appear to glow. (The phenomenon is known as fluorescence, not to be confused with the related phenomenon, bioluminescence.)