Scientists place cameras on sharks to watch them hunt for seals in a kelp forest

The tall, undulating algae known as kelp grow in thick underwater forests off the south coast of Africa. It was once thought that kelp forests provided a refuge for Cape fur seals from great white sharks. The researchers then installed high-resolution GoPro cameras on predators.

Instead of being discouraged by underwater flora, researchers find that sharks dive directly into thick kelp forests in search of prey. This is a new discovery for shark researchers, who had previously thought that forests were forbidden to hungry sharks.

"This is a completely new perspective of what they are doing," said Oliver Jewell, marine biologist at Murdoch University in Australia, who led the new research.

Long linger

The great white sharks are ambush hunters. They usually kill seals at dawn or dusk while pinnipeds swim to and from rocky outcrops. However, in previous research, Jewell and his colleagues had discovered that near Dyer Island, a reserve on the southern tip of Africa, sharks wandered all day near seal colonies.

"We wanted to know why but it was difficult to be sure we did not see what the sharks were doing under the surface," said Jewell.

Researchers combined HD video cameras with eight sharks while 9 to 12 foot predators swam freely in the water, ensuring that the perfect viewing angle is maintained. They could see what the sharks could do under the surface. Each camera recorded eight hours of footage in broad daylight for one to three days before depositing the animals.

Agile navigation

Video footage and camera tracking data revealed that forests do not deter predators. Almost all sharks have moved several times in the dense kelp jungle, researchers report today in the newspaper. Royal Society Biology Letters. A shark has even spent the majority of his time in the thick canopy.

The results call into question earlier work. "A previous study found that Cape fur seals were taking refuge from white sharks in the kelp forest," Jewell said. "What we have found is that white sharks enter the kelp forest after them and are more than able to navigate in and search for food in and through dense kelp . "

But even entering the seal hiding place does not guarantee a meal. Seals avoided sharks with expert hijacking tactics. They blew bubbles, swam deeper in kelp or squatted near the seabed. Avoidance strategies have proven effective. None of the sharks managed to catch a seal during the study, although this may simply be due to the fact that successful catches are quite rare in general.

That said, Jewell said, "It has been a great find and an incredible feeling" to film a camera attached to a shark.