Great whites face extinction

 

 

Sheree Bega

Cape Town - It's not easy to find great white sharks, never mind count them. That’s why it took Dr Sara Andreotti and her colleague “Shark Man”, Michael Rutzen, more than six years of painstaking research gathering “shark fingerprints” and DNA samples to understand the crisis facing the iconic predatory species.
The results of their pioneering study, conducted with colleagues from Stellenbosch University, sketches a gloomy picture for the survival of South Africa’s king of the oceans: there are only between 353 and 522 individual great whites left.

 

The great white shark population has been wiped out by shark nets, poaching for their fins and jaws as trophies, habitat encroachment, pollution and depletion of their food resources. Picture: Dr Sara Andreotti

Their research, the results of which were released yesterday, represents the largest field research study on great whites yet undertaken, but its conclusion is bleak: South Africa’s great whites are fast heading to extinction.
The famed sharks, says Andreotti, of the university’s department of botany and zoology, are in double jeopardy.
“Not only do these sharks have the lowest genetic diversity of all white shark populations worldwide, there are also only between 353 to 522 individuals left.”
This is 52 percent fewer than was estimated in previous similar studies, which listed the great white shark population in the low thousands.
Sometimes, Andreotti and Rutzen lived at sea for as long as two months – the Italian researcher battled fierce waves of seasickness.
Rutzen, a shark behaviour specialist with Shark Diving Unlimited, used his knowledge to track the elusive animals in Gansbaai, the heart of South Africa’s shark diving industry, and all along the country’s coastline.
Between 2009 and 2011 they collected nearly 5 000 photographs of the dorsal fins of white sharks frequenting Gansbaai.
It was Andreotti who manually organised almost 5 000 photos of their dorsal fins – a unique fingerprint that has a specific number of notches on its trailing edge – into a database, specifically documenting the date when an individual was sighted again.
To their dismay, once 400 individuals had been identified, they struggled to find new individuals to photograph.
“I remember there was one day in Gansbaai where we could sample 17 sharks, but that only happened once in five years,” explains Andreotti.
“Normally we took one sample once a day. There were not a lot of sharks. They all have different personalities, but they are very skittish, although there were a few that were bold and wanted to come and play.”
The researchers had to be certain the white sharks that they identified and counted in Gansbaai were representative of the entire white shark population along the coastline.
They spent another four years sailing along the coastline, collecting biopsy samples and photographs of dorsal fins. The subsequent genetic analysis then proved that there is only one population and that the same sharks are roaming the coastline.
Andreotti blames the impact of shark nets and baited hooks implemented on the eastern seaboard of South Africa as a major contributor for the decline in numbers of great whites.
“For example, between 1956 and 1976, the number of large sharks caught in KwaZulu-Natal’s shark-netting programme declined by over 99 percent. Between 1978 and 2008 about 1 063 white sharks were killed in shark protection measures,” she says.
A Stellenbosch University team has developed the Sharksafe Barrier, which is an environmentally friendly artificial magnetic kelp, says Professor Conrad Matthee, the head of the department of botany and zoology at the university.
The KwaZulu-Natal Sharks Board has invested in a similar shark-repellent system, he says. “There is huge pressure to stop shark nets around the world…
"Part of the reason rhinos get more attention than great whites is because of the fear of sharks – they are seen as killing machines and have to fight that much harder for protection.”
Poaching, habitat encroachment, pollution, depletion of their food sources and illegal poaching for trophies (jaw sets and fins) are other reasons for the sharp decline in the local great white population.
“If the situation stays the same, South Africa’s great white sharks are heading for possible extinction,” warns Andreotti.
Previous research on other species indicate that a minimum of 500 breeding individuals are required to prevent inbreeding depression, she adds. A delicate and complex balance exists between the ocean and its inhabitants.
“Sharks, as top predators, are particularly important as they directly influence the population size of prey communities, as well as prey behaviour and space use. The problems stemming from the loss of apex predators are complex, but quantifiable negative implications for the marine ecosystem have been reported,” she adds.