Predatory behaviors of great white sharks deep into the water are unknown to man. Whether they hunt for preys or swim peacefully underwater is a question that seems impossible to answer via direct observations by humans.
Fortunately, an underwater robot installed with REMUS SharkCam, was able to record footages of sharks, paving the way for better understanding of the species' behavior below the water surface.
In November 2013, the autonomous underwater vehicle (AUV) installed with six high-definition cameras sailed off Mexico's Guadalupe islands where sharks are known to gather massively. The main goal was to understand how white sharks behave.
"Most of what we know about white shark predatory behavior comes from surface observations," said lead researcher Greg Skomal from Massachusetts Division of Marine Fisheries. To know what happens at depth, researchers need a specialized tool and for Skomal, that is the REMUS AUV.
For Woods Hole Oceanographic Institution (WHOI) engineer Amy Kukulya, who is also one of the principal researchers, the team wanted to prove that the REMUS SharkCam technology is an essential modality for observing animals and obtaining information about the animals' habitat and behavior.
The animal behavior captured by the videos range from simple nudging to strong bumping of the vehicle. The bumps were said to be a form of aggressive behavior, comprising of short physical interaction, most commonly characterized by the shark nudging the vehicle with its snout.
In nine instances, the researchers noted aggressive bites, which are said to be a predatory behavior. The bites typically took place at the rear of the vehicle.
"Predation events are rarely witnessed," the authors wrote. Almost all recorded predatory actions were observed on water surfaces. In the expedition, however, predatory behavior on the surface was rarely seen. The researchers hypothesized that maybe Guadalupe's clear waters pose varying hunting opportunities for the sharks.
For example, sharks may stalk preys from deeper parts of the water where it is darker. Because of the island's visible waters, the sharks are able to see its prey's silhouette and attack it from below.
The expedition consisted of six AUV missions that were performed for a period of seven days. During that time, the experts were able to tag and track a total of four sharks, collecting 13 hours' worth of video data. Among the shark species observed were one male and three female great white sharks, including a 21-foot Deep Blue from 100 meters or about 328 feet deep under.
While the main animal being observed was the great white shark, the video was also able to capture footages of animals that were not being tracked. All in all, the investigators were able to record 30 interactions with 10 individual sharks.
The expedition marks the first successful endeavor to autonomously track and capture any marine animal. The data gathered in the experiment may pave the way for better conservation measures that the marine animals need for survival.
The REMUS AUV was initially created to aid coastal mapping and monitoring projects. As more versions were released, the developers were able to customize the vehicle for other purposes.
The REMUS SharkCam is equipped with salinity and temperature probes, water current detectors, six HD cameras and other sensors to enable observations from various angles and perspectives.
The findings of the expedition were published in the Journal of Fish Biology.
