This year marks the 10th anniversary of National Geographic’s Sharkfest, and the NatGeo channel is celebrating the occasion with an intriguing new documentary exploring whether great white sharks can change color to hunt more effectively. camouflage sharks follows on-site marine biologist and research coordinator for the Blue Wilderness Research Unit Ryan Johnson and graduate student Gibbs Kuguru as they attempt to gather evidence to support the hypothesis that these marine predators can tweak the skin cells in their skin to enhance color change camouflage.
Born in New Zealand, Johnson grew up in a beach town and embraced the popular belief 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 20 years old, he had the opportunity to conduct research on great white sharks in South Africa, which at the time were under tremendous pressure from overfishing, leading to an increase in shark attacks.
“They had just become very popular as a delicacy,” Johnson told Ars. “The shark fin soup trade had gone crazy, and [sharks] were massacred. For me it was an awakening of consciousness. I realized that this requires attention, at least from my point of view, much more than with dolphins.”
Since then, Johnson has investigated questions about whether the great white shark cage diving industry is making sharks increasingly dangerous to humans and has conducted satellite and acoustic tracking of great white sharks. He has also studied the impact of ecotourism on sharks, studied great white shark bite force, and studied predator-prey games between great white sharks and the seals they hunt.
Because of his field experience, Johnson had long believed that great white sharks could change color. Shark researchers identify certain animals based on their dorsal fins, scars, and other distinguishing features. He recalled that he and his team would often spot one light-colored shark in the morning and another, duller shark in the afternoon, assuming they were two different animals. “But then you would go back and look at the photos and be like, ‘Ah, that’s not a new shark. This is the same. The dorsal fin marking is the same,’” Johnson said.
Then he met Gibbs Kuguru, who was doing his PhD on color changes in blacktip sharks in the Maldives. “I said, ‘Hey man, what if I told you great whites change color too?'” Johnson recalled. Kuguru thought the idea sounded intriguing, and the couple began researching the topic. For example, they found instances of sunbathing hammerhead sharks and certain rays that could change color.
Other previous studies have found that zebra sharks change color as they age, and rainbow sharks sometimes lose their color due to stress and aging. And as we reported in 2019, a new family of small molecule metabolites is found in the lighter parts of wave shark skin (Cephaloscyllium ventriosum) and chain catsharks (Scyliorhinus retifer) allow them to absorb blue light in the ocean and turn the light essentially green, making them appear to glow. (The phenomenon is known as biofluorescence, not to be confused with a related phenomenon called bioluminescence.)