South Africa’s once-abundant yellowfish are being wiped out by acid water, sewage and invasive species

South Africa’s once-abundant yellowfish are being wiped out by acid water, sewage and invasive species
Members of the SANDF and officials at a sewage treatment plant on the Vaal River during clean-up operations on 1 December 2018. (Photo: Gallo Images / Sunday Times / Alaister Russell)

There has been a ‘massive change’ to the country’s yellowfish population. And unless South Africa cleans up its rivers, a species that was once common could become severely threatened.

India has its mahseer, Mongolia the taimen and South Africa the yellowfish – all sporting fish that have become highly sought after by anglers.

In South Africa, the pursuit of various yellowfish species caught with fly rods has evolved into an industry worth hundreds of millions of rands. It is a species that is now also attracting international visitors.

But what happened in the lower Wilge River in Mpumalanga last month shows that even species that are relatively common can become severely threatened in a short time.

About 58km of the Wilge River was killed off after millions of litres of acid water was allowed to flow into the waterway from an old coal mine owned by Thungela Resources. The wastewater came from Khwezela Colliery’s Kromdraai site, outside eMalahleni.

Tonnes of fish were killed and aquatic vegetation wiped out. It will take years for the river to recover.

The Vaal River is home to two yellowfish species, the smallmouth (Labeobarbus aeneus) and the largemouth yellowfish (Labeobarbus kimberleyensis). And although they are not on the Red Data list for threatened species, Dr Gordon O’Brien, a senior lecturer at the University of Mpumalanga’s School of Biology and Environmental Sciences, says their numbers have declined.

“We used to do our yellowfish population and health work around the Barrage area, just south of Joburg. We used to spend days and days processing fish because there were just so many, the abundance was incredible.

“Now you don’t find any largemouth yellowfish there any more. And if you [went] down to Parys, the largemouth yellowfish population was so massive. So, in the past 15 to 20 years we have seen a massive change.”

O’Brien added that 70% of the fish’s habitat had been destroyed. “They’re particularly vulnerable because of multiple stressors affecting the water resources.”

Stressors include a constant flow of sewage into the Vaal River and, like in the Wilge, acid water being released by large industrial plants. The acid water spills, however, have not been as severe as they were in the Wilge River.

“The Rietspruit in Sebokeng is the worst area. It has about 500 times greater than the maximum acceptable level of E. coli [determined] by the World Health Organization,” said Chris Williams of Save the Vaal Environment (Save), an organisation that is advocating for South Africa’s second-largest river to be protected and cleaned up.

The sewage flows into the Vaal River because wastewater treatment centres are not functioning properly, or have been damaged by theft.  

Besides pollution and acid water drainage, the Vaal’s indigenous fish species are also under threat from invasions of alien species.

Grass carp that come from China are becoming more common in the Vaal system, and can grow to 45kg. Largemouth bass have also established themselves in the river. These new species not only compete with indigenous species, but also bring diseases with them. Save recently reported that an exotic aquatic plant, known as water lettuce, had been found in the river. Water lettuce forms dense mats that cover and clog a water surface and reduce water flow, reducing oxygen in the water.

What is surprising about yellowfish is that there is still much to learn about it. There are nine different species in South Africa and this, thanks to genetic testing, could soon change.

The diversity between various yellowfish species in the Vaal River, O’Brien said, means that eventually they could be separated into new subspecies or even species.

The smallmouth yellowfish (Labeobarbus aeneus). (Graphic: Supplied)

But, with the declining state of the Vaal River, conservationists and citizens are becoming concerned. Politicians and officials, they say, offer little more than empty promises to clean up South Africa’s rivers.

The South African National Defence Force was brought in to clean the Vaal River in 2018. Two years later, the deployment ended. Nothing had changed, Williams said.

Now activists have hit on a new tactic they hope will get results.

“You’ve got no interest at all from local municipalities or higher up. You’ve got no accountability for people breaking the law, which is where we at Save are [making] people accountable. The only way to do this is to get these guys in court, and they don’t like it,” said Williams.

The recent appointment of Senzo Mchunu as water affairs minister offers a glimmer of hope. In October 2021, he told residents in the Vaal area that sewage spills and contaminated water would soon be a thing of the past.

On the river, usually with a fly rod in hand, Mark Yelland can be found guiding clients to some of the best fishing spots.

Yelland has a deep love for the Vaal. He fished the river 40 years ago, when it was still safe to drink mouthfuls of its water.  

He has seen fish die-offs and felt the tingle in his fingers from industrial spills in the Vaal.

“If we have fewer fish or not, that is a debatable issue,” the professional fishing guide said, explaining that it is difficult to get a handle on fish numbers in the Vaal.

Slightly fewer fish numbers, he suspects, could be because of overfishing by fly anglers. Most fly anglers release the fish they catch back into the river, but their presence could be forcing the fish to go elsewhere.  

“Despite man’s best efforts, the Vaal has always bounced back – but how long can it keep doing this?” says Yelland. DM168

This story first appeared in our weekly Daily Maverick 168 newspaper which is available for R25 at Pick n Pay, Exclusive Books and airport bookstores. For your nearest stockist, please click here.

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