08 February 2006

The epic odyssey of a Great White Shark

A female great white shark tagged in waters off South Africa has completed the first known transoceanic trip for an individual shark.

According to Swiss marine biologist Michael Scholl, leader of the South African White Shark Trust (WST), Ramón Bonfil of the New York based Wildlife Conservation Society (WCS) and a number of other organisations, the shark travelling more than 20,000 kilometres to the coast of Australia and back again.

The epic odyssey of Nicole (named after the 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. Nicole not only travelled farther than any other known shark but completed the trip from South Africa to Australia and back in just less than nine months, the fastest return migration of any swimming marine organism known.

In 2001 a genetic relationship was established between Australian and South African white sharks and was published in the journal Nature. Dr. Ramón Bonfil, WCS researcher shark expert and leading author of the study said "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. 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, with funding from Project AWARE 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 devises and seven more with real-time satellite tags during this study. 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 980 metres (a record for white sharks) while crossing the Indian Ocean, she spent most of her time swimming along the surface, leading researchers to suspect that perhaps great white sharks use celestial cues for transoceanic navigation.

99 days later, Nicole was swimming about two kilometres 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 11,100 kilometres - 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 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. Thank to a number of grants from Project AWARE Michael has been able to identified over one thousand different white sharks since 1997, he says "Nicole with her regular visits to South Africa every year since 1999 between the months of June and December, is certainly one of my favourite sharks, and this pattern may also suggest that she might be travelling from South Africa to Australia and back every year, an amazing journey" adds Michael Scholl.

Nicole's complete journey of more than more than 20,000 kilometres is by far the longest distance travelled by any shark known to science. By comparison, a whale shark tagged in the Gulf of California was tracked with a satellite transmitter travelling some 13,000 kilometres 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 metres 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, but extensive research projects like the one conducted by the White Shark Trust in South Africa are addressing these key knowledge gaps. "Since 1997, I initiated an ongoing and continuous population research project on white sharks around Dyer Island, and I developed a new techniques that allows researchers to individually identify these sharks using photographs of their dorsal fins, called fin-printing, similar to human finger printing" said Michael Scholl of the White Shark Trust.

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.

Find out more about how you can help protect the sharks visit http://www.projectaware.org/uk/english/pts.asp

Source: Project AWARE


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