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Shark Info   (03-27-2002)




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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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Distribution of white sharks is influenced by their gender

Report by Shark Info

The migratory behavior of sharks is important when it comes to their protection. This study examines the migratory patterns of white shark populations in coastal regions off South Africa, Australia and New Zealand using parts of the mitochondrial DNA in analysis methods.

Mitochondria are cell organelles with their own DNA which in most animals can only be passed on to the next generation through the females, i.e. through the eggs, a characteristic which also applies to sharks. The examination of this DNA molecule reveals the pure female genetic line. As opposed to the mitochondrion DNA, half the DNA of the cell nucleus is passed on from the mother (via the egg) and half from the father (via the sperma). By examining such core DNA one can determine maternal and paternal genetic lines.

The analysis showed statistically significant differentiations with the maternally-inherited mitochondrial DNA among the three shark populations from South Africa, Australia and New Zealand, leading to the conclusion that female white sharks migrate and reproduce very rarely between these three countries.

Nevertheless, analysis of the bisexually inherited core DNA showed no significant differences between the populations (52 animals were investigated for Australia and New Zealand, and 43 for South Africa). Based on these results, the authors concluded that females tend to stay relatively loyal to a region. Males, on the other hand, rove in genetically effective numbers in the world's oceans, mating in Australia as well as in South Africa with resident females. These findings are fundamental for the international protection of white sharks. Such protective measures are only viable when based on a gender-determined distribution potential. Very seldom and only by chance are overfished local populations enhanced by immigrating females.

Source: Nature Vol. 412, July 12, 2001, Pages 139-140

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