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Shark Info 1 / 02   (03-27-2002)

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CITES

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Sharks and CITES

Dr. Thomas Althaus

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Sharks in Research and Industry

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Distribution of white sharks is influenced by their gender

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Extended niche for the white shark

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E. Ritter leaves Shark info and Shark Foundation

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Extended niche for the white shark

Report by Shark Info

The distribution of the white shark is global and based on today's knowledge especially concentrated on the continental coastal regions of moderate zones. New electronic tagging procedures make it possible to continually register and study the movement patterns of sharks over extended time periods.

Transmitters are fastened to the shark's back muscles. In two-minute intervals these electronic devices register water pressure (including water depth), temperature as well as daylight in order to measure the geographical zone. At a preset time, the transmitters are released automatically from the animals, float to the ocean's surface and transmit the acquired data via the Argos satellite system to a central computer which then forwards the data to the researchers.

Six adult white sharks were tagged with a transmitter off the coast of Central California. Data was collected from a period between 15 days and 6 months, from October to May. Initially the animals remained in the coastal area at a depth of 30 meters and water temperatures ranging between 10 to 14°C. Four sharks, which were monitored between four and six months, swam into the open sea where they stayed for the remaining time. Ninety percent of the time all four of them stayed in two regions, at a depth ranging between 0 to 5 meters and 300 and 500 meters. As the animals swam southwest, the maximum water depth constantly increased. Water temperatures at the surface varied between 20 and 26°C, in deeper waters between 4 and 8°C. White sharks thus tolerate a wider scale of temperature spectrum than up until now known.

One of the tagged animals, shark number 5, swam from the coast of Central California to Hawaii in 40 days at a minimum distance of 71 km per day. Although white sharks are seldom seen near Hawaii, the animal stayed there almost 4 months at a preferred depth between 0 and 300 meters.

Results show that white sharks spend more time - about 5 months - pelagic, i.e. in the open sea, a figure which is much higher than presumed. Whether their migratory behavior, including deeper dives, are connected with the search for food and/or with reproduction remains unclear. According to the authors, additional electronic taggings are needed to increase both the understanding of sharks' choice of habitat and knowledge of their migratory behavior, which in turn will provide critical data for the protection of white sharks.

Source:: Nature, Vol. 415, 3. Januar 2002, pp 35 - 36

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