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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