In 2012, when state shark scientist Greg Skomal and Woods Hole Oceanographic Institution engineers Amy Kukulya and Roger Stokey first envisioned tracking and filming great whites underwater using a self-propelled torpedo, they worried about disturbing the natural movements and activities of these huge predators.

What they didn’t anticipate was that the REMUS, at about 6 feet long and weighing around 80 pounds, would become the prey, surviving nine attacks and four bumps by great whites weighing thousands of pounds during a week of research in 2013 off Guadalupe Island in Mexico.

Video: See up-close shark video from WHOI's REMUS "SharkCam"

In a world where there is very little documented about the life of great white sharks, you take what you can get. While they weren’t what researchers anticipated, the attacks on the REMUS at around 160 feet below the surface mark the first time such predatory behavior has been filmed deep underwater.

In a paper recently published in the Journal of Biology, co-authors Skomal, Kukulya, Stokey and Mexican shark researcher Edgar Mauricio Hoyos-Padilla, described how the hunter got captured by the game, as the torpedo they hoped would document a predatory attack on a seal or other marine animal became an unintended lure that attracted great whites and then recorded the attack in a panoramic view on six high definition underwater cameras.

“I was extremely surprised by it,” Skomal said of the REMUS’ mysterious appeal as a potential meal for so many of these sharks.

“We didn’t expect it at all. When it started happening we were all shocked by the ferocity and behavior of the animal when it struck,” he said. Bites lasted as long as 15 seconds, with the heavy torpedo forced upward 10 feet on impact.

To follow the sharks closely, Kukulya and Stokey installed a navigation system onboard the REMUS autonomous underwater vehicle, which is made in Pocasset by Hydroid, Inc., that exchanges signals with a transponder attached to the shark by a harpoon with a detachable tip. The REMUS is self-propelled and uses the locator signal from the transponder to find the shark, then follow at a distance scientists believe will not alarm it or change its behavior, but will still permit the cameras to obtain high-quality video images.

Funded by the Discovery Channel, with support from WHOI, the Massachusetts Division of Marine Fisheries and Pelagios-Kakunja of Mexico, the drone setup was first tested on the Cape in 2012 with basking sharks and then with great white sharks off the Outer Cape, following closely behind in shallow water with little interaction.

But in Mexico scientists believe the torpedo entered a “kill zone,” a depth and distance from shore in which the white sharks felt the water was deep enough for them to hide and where there was enough prey, perhaps seals going to and from Guadalupe Island. Ten sharks were responsible for both the bites and the bumps that scientists said could be territorial or a way of determining whether REMUS was fit to be on the menu.

Great white sharks are visual hunters. The visibility is considerably better in Mexico, with 80 to 100 feet possible off Guadalupe compared with 2 to 20 feet in Cape waters. But that means great whites have to go deeper to remain undetected by prey. Scientists say they believe the sharks see their prey silhouetted against the sun and attack from below. The attacks on seals usually are to the hind section, biting off the rear flippers, immobilizing them, and then finishing off the carcass when it floats to the surface.

The 2013 tracking study data reveals that the four sharks tracked by REMUS spent 80 percent of the 13½ hours they were followed at depths greater than 300 feet and only 5 percent in water shallower than 80 feet. But the model REMUS used in 2013 was rated only to 328 feet and could not follow below that depth. The sharks dived as deep as 530 feet, so REMUS was left traveling overhead, in the kill zone.

In one of the videos, the rear-facing camera catches the shark as it ascends, gaining swiftly on REMUS. Its close-set eyes home in on its prey, and its jaw is slightly open in an eerie, enigmatic “smile.”

The attacks caused deep scratches in the metal housing toward the aft section of REMUS, as though the sharks were trying to immobilize a seal or fish. One mission had to be aborted when a bite punched through the metal, letting in water.

“It made sense to us that these were predatory attacks,” Skomal said. He said it was hard to tell exactly what the sharks thought they were attacking, and future studies may help determine what visual clues provoke an attack.

While scientists have figured out kill zones in other great white hot spots such as the Farallon Islands off San Francisco and Seal Island off Cape Town, South Africa, Skomal said that is still undetermined for Cape Cod. The Cape is distinctly different in having the shallowest waters of all the world’s hot spots. He says he does not believe there is much predation in our deeper offshore waters but that most occurs relatively close to land where it is more difficult to hide and attack from below. Instead, the poor water clarity around the Cape might make it easier to go undetected and attack at the surface.

“Each area is unique, but we haven’t quite worked that out for the Cape,” Skomal said. “(The kill zone) is driven by visibility and the behavior of the prey itself.”

In the next year or two, Skomal says researchers might have better answers for where attacks on seals take place and help pin down high-risk areas humans should avoid.

Skomal and the WHOI engineers returned to Guadalupe this past fall with a version of REMUS that could dive to nearly 2,000 feet.

“Our first major goal was to advance the technology,” Skomal said. “The ultimate goal is to apply it to the Cape and other areas.”

— Follow Doug Fraser on Twitter: @dougfrasercct