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The South African great white shark population is in bad shape. Very bad shape. Image: Shutterstock

The South African great white shark population is in bad shape. Very bad shape. Image: Shutterstock


The Inertia

South Africa is known for being one of the sharkiest places on earth. According to a team of researchers from Stellenbosch University, though, that image could be more wrong. The great white population there is close to extinction, with somewhere between 350 and 530 left. And it’s not just the low numbers that’s worrisome, either. There’s something else in play that puts the great whites in very dire straits: not only are their numbers alarmingly low, but the genetic diversity of those particular great whites is the lowest in the world.

“The numbers in South Africa are extremely low‚” said Sara Andreotti of the Stellenbosch University Department of Botany and Zoology. “If the situation stays the same‚ South Africa’s great white sharks are heading for possible extinction.”

Their findings aren’t just based on a few months of head counts, either. The study was the largest and most in-depth ever conducted in South Africa, at least according to Sunday Times. It took six years to complete, and was focused around Gansbaai, the most popular destination in SA for shark diving. Gansbaai, according to recent studies, basically holds all the genes for every great white one South Africa’s coast. A while ago, I wrote something about the genetics of South African great whites, which was based on another study done by Stellenbosch University. It found that the genetic diversity of those particular great whites is the lowest in the world. Here’s what I wrote about it:

“‘We found only four maternal genetic lineages in the South African population, with 89% of all the sharks sharing the exact same gene sequence,’ said Dr. Sara Andreotti, who headed the study as part of her doctoral research.

In case you didn’t read that properly, there are only four genetic lineages. FOUR. In the entire population of great whites off the South African coastline. So why should genetics matter? Well, it goes back to evolution, in a roundabout way. A bigger diversity means more chances for shark populations to fight off disease or environmental changes. Think of Alexei Nikolaevich, Tsarevich of Russia. The world’s most famous hemophiliac was rumored to have contracted the disorder through generations of inbreeding. In a diverse genetic pool, chances are far higher that poor little Alexei could have cut his knee or bloodied his nose and not had to worry about dying or running to Rasputin to get some herbs or whatever he gave him. Of course, that’s an extreme example, but you get the point: four genetic lineages in a huge (although dwindling) population of sharks is not a deep gene pool, and leaves any and all offspring exponentially more susceptible to being, well… weaker. And as an apex predator responsible for regulating a large portion of other species’ populations, weak is bad. Which, again, is bad for us. We should be looking out for the sharks, because that means we’re looking out for number one.”

In the most recent study based on finding out the actual number of sharks in the area, the team took almost 5000 photos of dorsal fins in a two year period, using the fins to identify different sharks. “Using mark-recapture techniques‚ the results from this part of the study indicate with 95% confidence a population estimate of between 353 and 522 individuals,” said Andreotti. That’s a staggering 52% lower than previous estimates.

Andreotti said something after their study on SA great whites that, while it’s based on genetic diversity, holds even more water with the results of their newest study. “It is obvious that current conservation measures should take the low levels of genetic diversity into account,” Andreotti concluded. “Otherwise, one of these days we will not have any white sharks left to worry about.”

 
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