Scientists Strap Cameras to Sharks to Watch How They Hunt Their Prey

Footage shot from cameras attached to sharks has revealed how the animals charge through underwater forests to hunt for seals in areas previously thought to be inaccessible to the predators.

Compared to land animals, it's relatively difficult to study the behavior of underwater creatures in great detail. To gain a greater understanding of how great white sharks navigate kelp forests off the coast of South Africa as they track down Cape fur seals, scientists lured sharks to a research boat. They then strapped cameras with motion sensors to eight of the predators.

Past research shows sharks ambush seals at twilight as they travel from the land to sea. But scientists are interested in the seals and sharks who inhabit the waters of the Dyer Island Marine Reserve at the southern-most tip of Africa, because they act differently.

The seals have lower levels of the stress hormone cortisol. And Dyer Island is the only seal colony in South Africa where sharks appear in the daytime, said the authors of the new study published in the journal Biology Letters. It is believed this is because seals can hide from their attackers in the kelp.

The resulting 28 hours of footage showed how the huge animals, each measuring between 275 to 365 centimeters in length, moved through dense kelp forests to chase down their prey. The researchers noted down moments in the footage including when a seal could be seen, and when the sharks touched or moved between small gaps in the kelp. Of the total, seven sharks repeatedly moved in areas thick with kelp, and four touched kelp fronds or stipes.

Seals, meanwhile, reacted to the approaching sharks by trying to hide among the plants, blowing bubbles, or getting low down on the sea floor.

Oliver Jewell, a marine scientist and PhD candidate at Murdoch University, told Newsweek: "It was previously assumed that kelp was a barrier to white sharks, and it's only through these relatively newly developed tags that we were able to observe it is not. It's a great example of how technology is being used to change our perspectives on the behaviors of wildlife."

Jewell, who has studied and tracked sharks previously, expected the animals to interact with the kelp to some extent but was surprised by how important the plant was to their hunting behaviors.

"[The video showed] all the sharks by the island went into it [the kelp] and then we got the interactions with the fur seals and the chase, which was amazing," said Jewell of the footage.

Collecting such footage is tough, admitted Jewell as he highlighted the limitations of the study.

"Even if you know where the sharks are, you need to get them close, you need to get these tags on safely, with a good POV angle, you need good visibility and then you need to get the tag back. And that's before you know if the shark is going to do anything interesting, most of the time they just swim.

"Our team have used these methods on white sharks at locations across the world but this remains some of the best footage we've ever captured."

The team has used this technique on animals in a number of locations in California, as well as Cape Cod. Next, they'll harness the approach in Australia in an attempt to build a global catalog of foraging practices, said Jewell.

"This study is really the tip of the iceberg in terms of what more we can learn about these animals using this technology," he said.

Documenting how predators like sharks hunt their prey is vital if scientists are to gain a deeper understanding of how Earth's ecosystems work. Researchers in California, for instance, have studied why great white sharks gather in huge groups in a 160-mile section of the middle of the Pacific ocean between Baja California and Hawaii, in the spring and winter.

The area was thought to be void of prey, but scientists found a spot just above the darkness of the deep sea was populated by tiny creatures. These in turn attract animals which sharks prey on. Scientists have dubbed the spot the White Shark Cafe.