Tagging of Pelagic Predators

A new app produced by the Stanford University research team allows users to detect the comings and goings of white sharks along the Northern California coast. The Shark Net app for iPhone and iPad brings users face to face with a variety of individual white sharks, and provides notifications when their electronic tags are detected by underwater listening stations.

For more than a decade GTOPP white shark researchers have been studying the migrations of white sharks, using a variety of cutting-edge electronic tags. Their research has shown that these sharks make migrations across thousands of miles, traveling to the Hawaiian Islands and to the “White Shark Café,” a place in the open Pacific about halfway between Hawaii and Mexico’s Baja Peninsula. But towards the end of summer the sharks return to the California Coast, to places like Tomales Bay north of San Francisco, the Farallon Islands 30 miles out from the Golden Gate Bridge, and Ano Nuevo, just north of Santa Cruz.

“Over the past 12 years we’ve learned where the hotspots are along our coastline,” says Stanford Professor of Marine Sciences Dr. Barbara Block, “These are very wild places, where white sharks come to feed on the seals and sea lions that congregate here.”

Armed with the knowledge of where the white sharks congregate, Block and her team began to use a new approach to studying the animals – using lower cost acoustic tags, which can be detected by strategically-placed underwater receivers. These tags, which can remain active for several years after being deployed on a shark, allow the researchers to detect individual sharks when they pass within 1000-1500 feet of a receiver. By placing receivers around the various hotspots they’ve identified, they can learn more about the timing of their migrations, and how they change from year to year, as well as better understanding patterns of residency and habitat utilization.

“For several months of the year, these hotspots along the northern California coast are like a local neighborhood for these sharks,” explains Stanford postdoctoral fellow Taylor Chapple. “They might hang out at one spot for a week or two, then spend a few days at a different spot, and then come back.”

After years of studying these animals, the research team has come to recognize individual sharks – based on the patterns of irregularities along the trailing edge of each shark’s iconic dorsal fin, as well as the patterns of marks and scars on their bodies. Some of the sharks have been given names to help keep track of them, like Tom Johnson or Scar Girl or Flat Top, and behind every name is a story.

Through the Shark Net app, users will be able to interact with a detailed 3-D model of several of these sharks, to see photos and videos of them from the research team, and to receive real-time notifications when one of them is detected by an acoustic receiver.

“The idea behind the app,” explains Stanford University marine biologist Randy Kochevar, “is to allow everyone to explore the places where these sharks live, and to get to know them just like their friends on Facebook or Google+.”

The app was created in collaboration with the software development companies EarthNC and GaiaGPS, both of which specialize in developing interactive marine mapping applications for education, management and conservation.

“The idea behind this project,” says Block, “is that by allowing people to make a personal connection with these animals, they can start to see the ocean the way that we see it as scientists. And we hope that through that experience they might be inspired to help protect it, just as we have done for some of the other special, wild places on the planet.”

The app is just one aspect of a more ambitious undertaking Block calls the Blue Serengeti Initiative. Launched this year, with the help of a Rolex Award for Enterprise, an International Cosmos Prize from the Expo ’90 Foundation, and a research grant from Discovery Communications, this initiative seeks to develop the tools and technologies required to monitor the California Current Large Marine Ecosystem, and to explore ways of ensuring that it remains intact for future generations.