Every winter, the population of great white sharks(Carcharodon carcharias) that roams and feeds along the coastline from Central to Baja California disappears deep into the Pacific Ocean—swimming for 30 to 40 days to reach a point approximately halfway between Mexico and Hawaii.
There’s not a lot going for this particular spot in the ocean. It’s about 3000–5000 meters deep, and pretty barren as far as foodstuffs go. But the massive sharks—which can reach lengths of nearly 22 feet—stay there from about April to July, clustered in an area smaller than Panama. When the males arrive, they start diving up to 200 meters, repeatedly, up to 150 times a day.
And what they’re doing is anyone’s guess. Salvador Jorgensen, and Thom Maughan, an engineer with the Monterey Bay Aquarium Research Institute (MBARI), teamed up to develop a camera tag that can record video in low light, chart depths and acceleration, track the shark’s location, and monitor tail beats like a FitBit counts steps—all while submerged under corrosive sea water, sometimes to depths of more than 1000 meters.
Maughan’s rigged up a prototype composed of an off-the-shelf camera used to film offroad car races, commercial animal satellite tags, and innovative workarounds like ultraviolet-B LEDs to keep microbes from gumming up the lens and the machinery. The battery has enough juice to power about 10 hours of video recording, and they’re working on an algorithm that would turn the camera on when the movement sensors detect the sharks start the strange diving behavior that says they’ve arrived at the white shark café (which would allow more effective deployment of the battery life).
The tag itself goes on the dorsal fin, which Maughan calls nature’s tripod. But getting a camera tag on a shark’s dorsal fin isn’t an easy task.
“We put out a silhouette of a seal that’s made out of outdoor carpeting, and we trail that behind the boat,” explains Jorgensen. “And pretty soon we’ll get some interest from the shark that will come up and investigate the decoy, and we reel that in—it’s a little like fly fishing,” he says—if the fish you’re after is enormous. When the shark is circling the boat, they reach over the side with a 12 foot applicator pole and release the camera tag’s clamp onto the dorsal fin. “It’s really exciting—but it’s hard, your adrenaline is pumping,” Jorgensen says.
The first time Maughan went out with a crew tagging these sharks, he says he was tasked with photographing sharks’ dorsal fins, which can help scientists ID the sharks. “My mind was not prepared for how big around it was,” Maughan says. “When it came out of the water I recoiled a bit—and I took a lot of pictures of the sky,” although he did ultimately get a few photos of the dorsal fin. “Holy cow, that’s a sizeable animal.”
Retrieving the cameras should be simpler—once the sharks return to the California coast in late summer, the tag is designed to fall off and float to the surface where a satellite transmitter powered by solar cells signals its location to the research team so they can retrieve it and the data it contains.
Maughan is testing the camera on swimming robots in the laboratory and in Monterey Bay, and in the fall they plan to do short tests on sharks when they return to the California coast after their annual pilgrimage. Then, in Fall 2017, they hope to roll out around 20 of these tags to start watching what is really going on at this mysterious shark gathering place in the middle of the Pacific.
“We’ve lived with this narrative of white sharks being these mindless vagrants,” Jorgensen says. “But the more you study them, you realize that they have these very particular patterns.”
“And this white shark café is one of the most intriguing and mysterious—what are they doing out there?”
Jorgensen’s work will be featured in a documentary called Blue Serengeti, airing during the Discovery Channel’s Shark Week.
(via Rachel Becker on Slate)