Tagging of Pelagic Predators

 

On April 20, the Schmidt Ocean Institute research vessel Falkor sets sail from Honolulu, carrying a team of scientists seeking to unravel the mysteries of the White Shark Café.

First described in 2002, the White Shark Café is a region of the Pacific Ocean, roughly the size of Colorado, which lies halfway between Hawaii and Mexico's Baja Peninsula. Each spring, white sharks which spent the fall and winter months just off the coast of California aggregate there, in a region where there appears to be little food. The reason why, however, remains a mystery. Could they be diving to a deep-water layer rich in food? Or might this be some kind of mating behavior, relying on the unusual clarity of the water to allow them to find mates? These are among the questions the scientists hope to explore.

Led by Stanford University Professor Barbara Block, the research team includes marine biologists and oceanographers from Stanford, the Monterey Bay Aquarium, MBARI, the University of Delaware, and the NOAA Office of Exploration. In order to carry out their investigation, the researchers will be accompanied by an incredible assemblage of cutting-edge tools. These include a sophisticated remotely operated vehicle, the ROV SuBastian, which can dive to depths of 4,500 m and record high-resolution video. There is the Slocum Glider – a free-swimming, torpedo-shaped robot carrying instruments to measure temperature, xxxxx and xxxx (I wasn't able to find specs for what the glider is carrying) through the water column. There will also be two Saildrones. These newly-developed platforms, which look something like a cross between a large surfboard and a futuristic, rigid-sailed sailboat, can scan below the surface with sonar, picking up schools of fish, shrimp, and other marine prey.

The Saildrones also carry acoustic listening devices, specially designed to hear the coded "pings" emitted by acoustic tags placed on 35 different white sharks before they left the California Coast. Used in combination with Pop-up Satellite Archival Tags (PATs) that were also attached to the sharks, and which are programmed to come to the surface just as the Falkor reaches the Café, the researchers hope to have an incredibly detailed map of the café - not only telling them where the white sharks are, but also providing a profile of the prey surrounding them, and the physical and chemical conditions throughout the entire region.

With all of this information at hand, the researchers hope, for the first time, to begin to understand how the white sharks' behavior relates to the marine environment in the Café, and to begin to unravel the mystery of why they travel there year after year.