Newswise — A female great white shark tagged in waters off South Africa has completed the first known transoceanic trip for an individual shark, traveling farther than any other shark known, more than 12,400 miles (more than 20,000 kilometers) to the coast of Australia and back again, according to the Bronx Zoo-based Wildlife Conservation Society (WCS) and other organizations in the most recent edition of the journal Science. The epic odyssey of Nicole (named after Australian actress and white shark lover Nicole Kidman) has astounded researchers and will change long-held notions about how these charismatic predators move through the world's oceans. In addition to traveling farther than any other known shark, Nicole completed the trip from South Africa to Australia and back in just under nine months, the fastest return migration of any swimming marine organism known.
"This is one of the most significant discoveries about white shark ecology and suggests we might have to rewrite the life history of this powerful fish," said WCS researcher Dr. RamÃ³n Bonfil, shark expert and lead author of the study. "More importantly, Nicole has shown us that separate populations of great white sharks may be more directly connected than previously thought, and that wide-ranging white sharks that are nationally protected in places such as South Africa and Australia are much more vulnerable to human fishing in the open oceans than we previously thought."
The story of Nicole began on November 7, 2003, when Bonfil and his colleagues from the Marine and Coastal Management Department of South Africa and the White Shark Trust attached a satellite tag to Nicole's dorsal fin as part of a large study on white shark migrations. The tags—specifically known as pop-up archival tags—record data on time, temperature, water depth, and light levels as the shark moves through its habitat. On a pre-recorded date, the tag detaches from the shark and floats to the surface, where it transmits its data sets to a researcher's computer via satellite.
An additional 24 white sharks were tagged with similar tags and seven more with real-time satellite tags during this study, with Bonfil and his team often having to wrestle the dangerous sharks while on a cradle in order to fix the satellite transmitters to their dorsal fins. While most of the tagged white sharks revealed at least three different movement patterns, including wide-ranging coastal migrations up and down the eastern side of South Africa, Nicole headed out into the vast and deep basin of the Indian Ocean. The track estimated from the data transmitted by the tag revealed that Nicole followed a strikingly direct route towards Australia, on a path void of oceanic islands. Although Nicole took frequent plunges to depths as great as 3,215 feet (980 meters—a record for white sharks) while crossing the Indian Ocean, she spent most of her time (61 percent) swimming along the surface, leading researchers to suspect that perhaps great white sharks use celestial cues for transoceanic navigation.
Ninety-nine days later, Nicole was swimming about a mile from shore just south of the Exmouth Gulf in western Australia, where her tag detached and floated to the surface with all of her secrets. This leg of the journey alone—some 6,897 miles (11,100 kilometers)—was one for the record books. However, Nicole would resurface again on August 20, 2004, not in Australian waters, but back in Gansbaai, South Africa, where she was tagged just under nine months before. Her distinctively notched dorsal fin was photographed by Michael Scholl, one of Bonfil's team researchers and compared to previous photographs he had taken over a period of six years. After a detailed comparison of images of dorsal fin notches and markings, there was no longer any doubt: Nicole had returned to her home waters. Nicole's complete journey of more than more than 12,400 miles (more than 20,000 kilometers) is by far the longest distance traveled by any shark known to science. By comparison, a whale shark tagged in the Gulf of California was tracked with a satellite transmitter traveling some 8,078 miles (13,000 kilometers) to the western Pacific.
"It's clear that we have only uncovered the tip of the iceberg; there is still much to learn about great white shark migrations, why and how they find their way through such vast distances, and how populations are related," added Bonfil. "More studies and funding are needed to unveil the mysteries of these great predators and how they can be protected in both national and international waters."
Reaching some six-and-a-half meters in length (21 feet), the great white shark is a member of the mackerel shark family, an assemblage of sharks that include the mako and the porbeagle. Traditionally, the great white was considered by the scientific community to be the most aggressive and dangerous of all shark species However, field studies have revealed that the great white shark is rarely a man-eater. Most attacks occur when great whites confuse humans with their preferred prey—sea lions, seals and other marine mammals. In fact, great white sharks, along with many other shark species, are now thought to be endangered by a combination of game fishing and commercial harvests for fins, which are highly sought in Asia's fish markets for shark fin soup. There are no exact figures on regional or worldwide populations of great whites.
The species recently received some global recognition as a persecuted species during the 13th meeting of the Convention on International Trade in Endangered Species of Flora and Fauna (CITES) in October 2004, when participants at the event adopted a proposal to improve management and monitoring of trade in jaws, teeth and fins from the world's largest predatory fish by placing the species on Appendix II.
The details of the field techniques used by Bonfil and his team to tag great whites in South Africa can be seen in the exciting documentary "Tracking the Great White Shark" (Apex Films, South Africa).
Photos of Nicole are available through WCS' Communications Office
Footage of WCS researcher Dr. Ramon Bonfil putting satellite tags on great white sharks is also available through WCS' Communications Office