'In-breeding' threatens South Africa's great white sharks

12 November 2015 - 20:21 By Farren Collins
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South Africa may be the rainbow nation‚ but our great white sharks certainly aren’t. A study has found that the genetic diversity of the South African white shark population is the lowest of all white sharks in the world.

Only four genetic groups exist in the South African great white shark population‚ and of those nearly nine out of 10 white sharks belong to the same group.

This kind of “inbreeding” among these already highly threatened fish‚ could seriously jeopardise their ability to survive in future‚ a Stellenbosch University research project found.

Dr Sara Andreotti‚ who headed the research‚ said: “We found only four maternal genetic lineages in the South African population‚ with 89% of all the sharks sharing the exact same gene sequence”.

“When compared with other marine species‚ it is even lower than that of the highly endangered bottlenose dolphin.”

Andreotti said the reason for the low gene pool was due to either increased killing of sharks or a historical local extinction and re-colonization process.

“Over 14 million years of evolution could mean that the local population could have gone through extinction‚ and re-population by white sharks from other parts of the world. We've seen this happen in other species of animal. The lack of genetic diversity could also be caused by the killing of these animals‚ and threatening of their environment through pollution and over-fishing.”

Genetic diversity in animal species is important for the species’ survival. A smaller gene pool makes a species susceptible to disease and vulnerable to unexpected changes in the environment.

“Disease will kill some individuals‚ but if there is a large genetic diversity‚ others with different genes or DNA will survive and continue to breed.”

The study was compared to similar studies conducted in Australia and the US‚ which found that white sharks there enjoyed “happier populations than those in SA because of greater diversity”.

Andreotti said more studies into the behaviour and migration patterns of these animals had to be done in order to find a solution to the problem.

Extinction of white sharks would affect the fishing industry as well as the marine environment.

“If you wipe out a top predator you have a negative cascade effect on the environment. It would cause an increase in Cape fur seals‚ and that would negatively impact the local fish population. Sharks also get rid of sick animals among fish and mammal populations.”

The Times

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