Great white sharks may change color when hunting prey: study

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Great white sharks may change color when hunting prey: study

Great white sharks are among the most feared predators, and some groundbreaking new research conducted off the coast of South Africa suggests these incredible fish found along coastlines around the world can change their color to hunt their prey better.

Sounds terrifying, right?

Officials stress that while shark attacks on humans are rare, they do happen.

This is especially true in the northeastern United States. New York and New Jersey beaches have experienced a string of shark sightings and attacks this summer, putting beachgoers on edge. 

Since the unofficial start of summer during Memorial Day weekend, beach officials have used drones, helicopters and beach closures to prevent a potentially deadly shark encounter after at least five people have suffered shark bites.

Still, when you look past the fact that these torpedo-looking fish weigh between 1,500 and 4,000 pounds and are armed with hundreds of sharp, pointed, coarsely serrated teeth that can rip apart flesh and bone to swallow their food whole, they’re fascinating creatures.

Great White Shark
A new study says Great white sharks may change their color when hunting prey.
Getty Images/iStockphoto

For starters, great white sharks have seven senses, including all the senses we use as humans: hearing, smell, vision, touch and taste.

But they have two others that set them apart from the rest: lateral line and Lorenzini, which NOAA Fisheries says were discovered within the past 10 to 20 years.

The lateral line is a strip of sensory cells that runs along the shark’s body under its skin and can detect the slightest vibrations in the water. It is beneficial when hunting for food or if a potential predator is nearby.

According to SharkTrust.org, sharks also have a complex electro-sensory system aided by receptors that cover the shark’s head and snout that sit in jelly-filled sensory organs called the ampullae of Lorenzini. This helps the shark detect faint electrical fields such as those generated by the Earth or muscle contractions in their prey.

It’s also believed that the Earth’s geomagnetic field is thought to help sharks navigate the world’s oceans and migrate long distances so accurately, according to SharkTrust.org.

The sneak attack

Sharks usually ambush their prey by rushing from near the ocean floor to the surface to surprise their next meal and inflict a large, often fatal, bite. After the animal is lofted into the air, the shark will retreat and wait for the animal to fall back into the water, continuing its attack and devouring its food.

But wouldn’t animals know a shark lurks below them while they swim along? New research suggests that sometimes sharks may be able to change their color to blend in with their surroundings.

Great White Shark
There have been multiple shark sightings and attacks at New York beaches this summer.
Getty Images/iStockphoto

How is that possible? Gibbs Kuguru had the same thought.

Kuguru is a shark scientist and PhD student at Wageningen University and Research in the Netherlands and conducts research into the fish’s skin.

“I began my research on the skin of sharks when I heard about some sharks in the Maldives that had developed a very peculiar skin deformity called leucism,” Kuguru said.

Leucism is a skin condition that results in the loss of pigmentation.

“The presence of leucism raised many questions that led me to investigate the causes of the deformity, which taught me a lot about the make-ups of shark skin and the different adaptations they may have,” Kuguru said.

And during his time working at a cage diving company with great white sharks, he started thinking.

“I would often hear people gasp, ‘Whoa! That shark just changed color!’” Kuguru said. “Every time it happened, I questioned whether or not it was real or if our eyes were playing tricks on us. Together with my mentor, Ryan Johnson, we decided to put this fisherman’s tale to the test.”

That’s when Kuguru and Johnson designed the experiment to determine if great white sharks do indeed change color.

The pair headed to a shark hotspot off the coast of South Africa, where the experiments would take place.

They created a grayscale color board that would float in the water behind a boat and used a decoy food source to bait the great white sharks. As the sharks breached the surface, they would photograph them against the color board.

“The color board was a game changer when it came to observing differences in the shade of the animal,” Kuguru said. “Still, the technique we used to ‘track’ the sharks that were around any given day is an old one we still use. This technique is referred to as ‘photo ID.’”

Great White Shark
The study found that Great white shark’s skin definitively reacted to hormones.
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Kuguru said the technique uses photos of sharks and their distinguishing features to identify ones that are continuously spotted near the boat.

“Sharks will usually stick around for some weeks, but occasionally, we get some highly residential great whites which we see over the years,” he said. “We normally give these sharks a name, and they are usually good candidates for tagging, depending on the project.”

Extraordinary find back at the lab

Tracking the sharks isn’t a simple task, though. Kuguru said his ability to locate great white sharks came from years of collaborative efforts between scientists, shark tour operators and local fishers.

“Without this, I would have never seen a single shark,” he said. “Once we found the sharks, it was up to me to get in the cage with my dart gun and get a tissue sample from the shark.”

Kuguru said the sharks would move fast, so gathering skin samples needs a steady hand.

“My shot has to be decisive in order to get the right tissue and also not to do harm to the shark,” he said.

Time was of the essence once the sample was collected.

“With the tissue samples from the sharks, we had to rush over to the laboratory in order to get confirmation that these sharks do indeed have the capability to modulate their color,” Kuguru said.

Back in the laboratory, testing was conducted on the shark’s skin.

“We did this by treating the skin with hormones that their skin cells would be sensitive to,” Kuguru said.

And the results were extraordinary.

“Interestingly, we not only found that the skin reacted to the hormones, but they did so in a strikingly, definitive way.”

The scientists watched as the shark’s skin would become darker when treated with one hormone, and would get lighter with another.

While this amazing discovery doesn’t fully determine whether great white sharks have the ability to camouflage themselves, it is an interesting find.

More studies and experiments will be completed to learn more about the exciting possibility.

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