Why Do Sand Tiger Sharks Form Gangs? | Shark Gangs

Off the coast of North Carolina lies a treacherous stretch of water with strong currents and shifting sands, with the remains of up to 5,000 ships. It's known as the graveyard of the Atlantic. Hidden within this eerie resting place for lost souls are gangs of sand tiger sharks. Photographer and conservationist Tanya Hoppermans has spent over a decade documenting the shark gang phenomenon occurring here.

"I started diving around 2009, came down here to North Carolina, and that was the first time that I saw the sand tiger sharks. It literally changed my life. I walked into work and quit, and left the corporate world behind and decided to devote my life to spending time with sharks."

Working with Spotif Shark USA, Tanya is studying the thousands of sharks that have made these shipwrecks their home. These rusting hulks provide the perfect conditions for marine life to grow and for predators to hunt. But why sand tiger sharks congregate here in such large gangs is still a mystery.

"There are times that we could see a hundred and maybe even more sharks in an aggregation. They really seem to prefer to be around other sand tiger sharks. We're not quite sure why yet."

Today, Tanya and her husband Scott are looking for answers by diving a wreck known for large groups of sand tiger sharks.

"Today we're heading out to the wreck in the Caribbean. This is a freighter that was sunk by a U-boat during World War II. Right now she lies about 90 feet underwater; that's where we tend to see a lot of sand tiger sharks hanging out."

Tanya is on the front line trying to discover the secret that unites these sharks. She's taking photographs so scientists can study them for vital clues.

"Inside this housing is the camera that I use to photograph the sharks, and we have two lasers here on each side. When I take a picture of a shark, these two green dots will show up on the side of the shark. We can then actually calculate the length of that shark just from the photograph itself. Then we can go in and identify each individual shark based on its unique spot patterns. It's like a fingerprint as to a person."

[Music] "I'll kind of give each other's gear a look over."

"All right, looks good."

Every dive has the possibility of learning something new about these animals.

"There really hasn't been a lot of research done on them, you know, compared to a lot of other species such as great whites. So, anytime we get in the water with them, and bring back any information for the researchers that I work with, it's a great day."

"Good food, great find, some sharks. We have 100 feet of visibility, clear blue water. A lot of the wreck is still intact. You can see the big bow structure. It never gets old."

"There are just sharks as far as I can see all around me. These sharks are named after tigers because of their voracious appetite, but to Tanya, they're gentle giants. They have these raggedy teeth that make them look really fierce, but these sharks are full of personality."

"Sand tiger sharks are probably about six or seven feet, so females being a little bit bigger than the males."

Surrounded by a swarm of sharks, Tanya begins her search for evidence as to why so many are here.

"There are a lot of females; every so often you see a few males, but it's mostly females. Why is that?"

With her laser-guided camera, Tanya captures her first clue to solving this mystery.

"Some of the females do have scars from mating. When sharks mate, the male actually holds on to the female with his teeth. If we see fresh mating scars, that female may be pregnant. We're finding several pregnant females."

"Why are they grouping together?"

"After photographing the girl gang, that was amazing; there were a lot of sharks."

Tanya tries to make sense of this incredible spectacle.

"So, what we're seeing is a big gang of sand tiger sharks—mostly females. We have so many unanswered questions, but what we're thinking is that maybe these females are aggregating together during pregnancy so that the males don't try to mate with them again."

"It could be possible that the females are kind of banding together; it's kind of a support network. They are choosing to group together like this. Not all sharks are just solo predators; sharks could have a social life just like humans."