This year marks the 10th anniversary of National Geographic’s Sharkfest, and the NatGeo channel is marking 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 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 tweak the dermal cells in their skin to change color as a means of camouflage.
A native of New Zealand, Johnson grew up in a beach-side town, absorbing 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 20, he had the chance to do some research on great white sharks in South Africa, which were facing tremendous pressure at the time from over-fishing, leading to a rise 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 getting mass slaughtered. It was an awakening of awareness for me. I realized this needs attention, a lot more so from my perspective, at least, compared to dolphins.”
Since then, Johnson has studied such questions as whether the great white shark cage-diving industry makes sharks increasingly dangerous to humans and has conducted satellite and acoustic tracking of great whites. He has also studied the impact of eco-tourism on sharks, investigated the bite strength of great whites, and studied predator-prey games between great whites and the seals they hunt.
Johnson had long thought that great white sharks might be able to change their color based on his field experience. Shark scientists identify specific animals by their dorsal fins, scars, and other distinguishing marks. 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 would assume they were two different animals. “But then you’d go back and look at the photos and think, ‘Ah, this isn’t a new shark. This is the same one. The dorsal fin marking is the same,'” said Johnson.
Then he met Gibbs Kuguru, who was conducting his PhD work in the Maldives on color changes in blacktip sharks. “I said, ‘Hey, man, what if I told you great whites also change their color?'” Johnson recalled. Kuguru thought the idea sounded fascinating, and the pair started researching the topic. They found cases of sunbathing hammerhead sharks and certain rays that could change their color, for instance.
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 ventriosum) and chain cat sharks (Scyliorhinus retifer) enable them to absorb blue light in the ocean and essentially turn the light green, making them appear to glow. (The phenomenon is known as biofluorescence, not to be confused with a related phenomenon, bioluminescence.)