What Sharks Are Tag-Teaming Attacks? | SharkFest

NARRATOR: Historically, shark attacks on Reunion have been rare. Over the previous decade, the annual average was just one incident. But in 2011, the island is in crisis. Mathieu is actually Reunion's fifth victim this year. And it's only September. Islanders are in shock. It's vitally important that we find out the reasons for these attacks. There is a real problem here.

LORIS GASBARRE: We noticed that something was changing. What? We didn't know.

NARRATOR: Residents are desperate for answers. Their safety and their livelihood is at stake.

LORIS GASBARRE: A small island lives with tourism. If we don't have tourism tomorrow, we'll have nothing left.

NARRATOR: So what's triggering this deadly spate of attacks? To find out, the French government calls in leading shark expert Geremy Cliff. Clearly, alarm bells were signaling. Five shark attacks, of which two were fatal. That is a huge spike.

NARRATOR: Cliff believes the first step to solving this mystery and preventing further attacks is to identify the species responsible. So he starts by analyzing Mathieu's incident. And a chilling detail stands out. He was attacked by two sharks.

MALE: [speaking french]

NARRATOR: A double shark attack like this is extremely rare. In fact, it's thought that such an event has only been captured on film once. In the year 2000 in South Africa, a teenager is surfing when he's suddenly knocked off his board by one shark, while a second shark attempts to bite him. Incredibly, the boy survives. But this tag-team tactic may serve as a calling card for the culprit in Reunion.

GEREMY CLIFF: Only certain shark species hunt together.

NARRATOR: Hammerheads search for food in large schools that can consist of more than 100 sharks. And lemons conduct coordinated assaults by herding prey into one area. Even blacktips hunt in groups in the shallows. But Cliff thinks these species are all too small to inflict the kind of damage that caused Mathieu's death.

GEREMY CLIFF: One of the striking features of this particular attack is the severe injuries involved.

NARRATOR: Such ferocity points to a much larger predator. And only two species commonly found in the region fit that bill.

GEREMY CLIFF: Firstly, we have the tiger shark. Tiger sharks reach at least 16 feet. They have the size, in terms of jaws and body size to be able to tackle large prey. And therefore, they won't be scared of attacking a human.

NARRATOR: Yet, Cliff doubts tigers are to blame. They are totally solitary animals and will hunt on their own.

NARRATOR: That leaves only one possible culprit. To explain, Cliff turns to footage recently captured off the coast of Reunion, as part of a study on the behavior of the region's sharks. It depicts one particular species that apparently plays well with others.

GEREMY CLIFF: It shows clear evidence of two sharks swimming together, one behind the other. In fact, in nearly 20% of occasions captured on film, they were seen foraging together. The sharks seen here are bull sharks.

NARRATOR: Bull sharks weigh as much as 500 pounds and are highly aggressive. They typically attack on their own, often head-butting prey before tearing it to shreds. But as these images reveal, they also use another hunting tactic.

GEREMY CLIFF: There's clearly an advantage to work cooperatively and thereby prove predation efficiency.

NARRATOR: Based on this evidence, Cliff believes he's identified the type of shark that killed Mathieu.

GEREMY CLIFF: So from that I would conclude that a bull shark was responsible for this particular attack.