This year marks the 10th anniversary of National Geographic’s Sharkfest, and NatGeo is celebrating the occasion with an intriguing new documentary that explores whether great white sharks can change their color to hunt more effectively. Camouflage sharks follows marine biologist and Blue Wilderness Research Unit research coordinator Ryan Johnson and graduate student Gibbs Kuguru in the field as they try to gather evidence to support the hypothesis that these ocean predators can tune their skin’s skin cells to change color as a means of camouflage .
Born in New Zealand, Johnson grew up in a coastal town learning the conventional wisdom that dolphins are the “good guys” and sharks are the “bad guys.” When he decided to become a marine biologist, he wanted to work with dolphins. When he was 20, he had the opportunity to do a little research on the great white sharks in South Africa, which at the time were under enormous pressure from overfishing, leading to an increase in shark attacks.
“They have just become very popular as a delicacy,” Johnson told Ars. “The shark fin soup business has gone crazy, and [sharks] were massacred. For me it was an awakening of consciousness. I realized that it requires attention, at least from my point of view, much more than dolphins.
Since then, Johnson has studied issues such as whether the 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 white sharks, and studied predator-prey play between great whites and the seals they prey on.
Based on his field experience, Johnson has long believed that great white sharks can change their color. Shark scientists identify specific animals by their dorsal fins, scars, and other distinguishing features. Often, he recalled, he and his team would spot a light-colored shark in the morning and another darker-colored shark in the afternoon and assume they were two different animals. “But then you came back and looked at the pictures and thought, ‘Ah, this is not a new shark. It’s the same one. The markings on the dorsal fin are the same,” Johnson said.
He then met Gibbs Kuguru, who was doing his PhD in the Maldives on the color change of blacktip sharks. “I said, ‘Hey man, what if I told you that big whites also change color?'” Johnson recalled. Kuguru thought the idea sounded exciting, and the pair began to explore the topic. For example, they found cases of hammerhead sharks and some rays that could change their color on fire.
Other past studies have shown that zebra sharks change color with age, and rainbow sharks can sometimes lose color due to stress and aging. And, as we reported in 2019, a new family of low molecular weight metabolites in the lighter parts of the skin of sea sharks (Cephaloscillium ventriose) and cat sharks (Sciliorhinus retifer) allow them to absorb the ocean’s blue light and turn it into light green, causing them to glow. (This phenomenon is known as biofluorescence, not to be confused with the related phenomenon, bioluminescence.)
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