For nearly 20 years, researchers from Monterey Bay Aquarium and Stanford University have fitted electronic tracking tags on adult white sharks each fall and winter along the California coast around San Francisco Bay. Each year, the tags documented a consistent migration by the sharks to a region more than 1,200 miles offshore—halfway to Hawaii—that’s been considered an oceanic desert. They dubbed it the White Shark Café, guessing that opportunities to feed and to mate might be the draw.
Now a team of scientists will spend a month at the Café in a month-long expedition to learn why the sharks make an epic annual migration to such a distant and seemingly uninviting location. The multi-disciplinary team is bringing an impressive complement of sophisticated oceanographic equipment, from undersea robots and submersibles to windsurfing drones that will search signs of sharks and their possible prey.
Funded by the Schmidt Ocean institute (SOI), the team is led by Stanford University Professor Barbara Block and includes marine biologists and oceanographers from Stanford University, Monterey Bay Aquarium, Monterey Bay Aquarium Research Institute (MBARI), the University of Delaware, and NOAA’s Office of Ocean Exploration and Research. They are traveling aboard the SOI research vessel Falkor and set sail from Honolulu on April 20. They will return to port in San Diego on May 19.
Unraveling a mystery
“We’ve studied these sharks for nearly 20 years, and they’ve told us consistently that the White Shark Café is a really important place in the ocean—but we’ve never known why,” said Dr. Salvador Jorgensen, a senior research scientist and shark research lead at Monterey Bay Aquarium.
By documenting the biology, chemistry and physical conditions in the region—a swath of the Pacific Ocean the size of Colorado—the researchers hope to understand what makes the Café an annual offshore hot spot for one of the ocean’s most charismatic predators.
“I think of it like Burning Man,” Sal says. “You have all these Bay Area white sharks, and every year they head out into this White Shark Café, out into the desert of the ocean—and we’re not exactly sure what they’re doing out there.”
That’s where the multi-disciplinary team and the ocean sampling equipment come into play.
High-tech research tools
The researchers are bringing a remotely operated vehicle, the ROV SuBastian, which can dive to depths of 4,500 m and record high-resolution video; a Slocum Glider—a free-swimming, torpedo-shaped robot carrying instruments to measure temperature, oxygen and salinity, through the water column; and two Saildrones. These newly developed robotic platforms, which are steered remotely and powered by the wind, can scan below the surface with sonar, picking up schools of fish, shrimp and other marine prey.
They will also use environmental DNA technology to help identify the community of animals using these waters.
To find the exact location of individual sharks present at the Café during the expedition, researchers hope to collect data from satellite and acoustic tags they put on the sharks during the fall and winter of 2017 off the California coast. The pop-up satellite archival tags (PSATs) are programmed to release from the sharks and report their locations beginning April 23—at the start of the Falkor’s journey. The Saildrones and Slocum Glider carry acoustic listening devices, specially designed to hear the coded “pings” emitted by acoustic tags placed on white sharks.
Shark tags reporting in
The pop-up tags detach from the sharks and feed their stored data to researchers via satellite, providing rich data sets on white shark locations and documenting their preferred water temperatures and swimming depths. Acoustic tags, which remain on the sharks, report the animals’ locations when they pass by a listening station—like a Saildrone or a Slocum glider.
Over 35 sharks are carrying tags. If all works as planned, some will release their pop-up tags in Café while the expedition is underway.
The researchers will compile all the data they collect—from tags, from shipboard instrumentation and from the robots—to generate a detailed 3-D view of the Café environment. This would tell scientists where the white sharks are, and document the oceanographic conditions and the prey surrounding them.
Stanford’s Barbara Block believes that understanding what makes the Café so attractive to white sharks will also reinforce its importance in the global ocean.
A 2016 report from the United Nations Educational, Scientific and Cultural Organization (UNESCO) and IUCN identified the White Shark Café as a potential World Heritage site, recognizing the unique importance of the region for white shark biology, she notes.
Dr. Block explains that, “By using the tools of modern oceanographic science we hope to better understand what makes this high seas place so attractive to one of the most iconic shark species on our planet.”