SA white shark population in jeopardy

2015-11-13 08:56


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2015-11-09 10:19

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Stellenbosch - South Africa's white shark population's capability to survive is in jeopardy.

This was because of a low level of genetic diversity, according to research conducted by the department of botany and zoology at Stellenbosch University (SU).

Research had been done on white sharks and their DNA along the South African coastline.

Dr Sara Andreotti, who collected genetic samples as part of her doctoral research at SU, said the genetic diversity of the white shark population in the country was the lowest in the world.

"We found only four maternal genetic lineages in the South African population, with 89% of all the sharks sharing the exact same gene sequence," she said.

"When compared with other marine species, it is even lower than that of the highly endangered bottlenose dolphin."

Andreotti was assisted by Mike Rutzen, a well-known shark conservationist, who tracked down white sharks along the coast line.

The field work took four years and by the end of 2014 they had collected more than 302 genetic samples and 5 000 photographs.

One common ancestral group

Genetic diversity was regarded as an important indicator of the resilience of a population in the wild.

The higher the diversity, the easier it was for a species to survive diseases or unexpected changes in the environment.

According to the research a completely different scenario emerged when all the individuals shared the same genetic information.

Andreotti said the research was on-going.

"The poor gene pool could be the result of a severe bottleneck or historical local extinction and re-colonisation processes.

"But our main and immediate concern now is to understand the potential negative effects the low levels of genetic diversity can have on South Africa’s white shark population."

The DNA of South African white sharks was compared with the DNA of 58 white sharks analysed in previous studies conducted in the world.

The results revealed that a unique lineage existed along the South African coast line that did not connect closely to other known lineage elsewhere in the world.

"It appears from this study that all white sharks originated from one common ancestral group in the Indo-Pacific Ocean around 14 million years ago," said Andreotti.

"Based on the data we could predict a west to east migration pattern and an ancestral link between the white sharks of South Africa and Florida. But we also found a unique South African female lineage that does not connect to any other lineage in the world.

"This means that it is either a very old lineage that formed in South Africa millions of years ago, or it might be linked with a white shark population that has not been sampled yet," she said.

It was still not clear whether sharks from this lineage carried some morphological or physiological characteristics which differentiated them from the common group.

The findings of the research had serious implications for the future management of the white shark population in South Africa.

"It is obvious that current conservation measures should take the low levels of genetic diversity into account, otherwise one of these days we will not have any white sharks left to worry about," said Andreotti.

Read more on:    cape town  |  marine life  |  conservation

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