Port Elizabeth is facing an extinction of indigenous fish in the Baakens River because of pollution, impassable infrastructure and invader species released by members of the public.
A Nelson Mandela University survey has revealed a river under siege, the water “rotting” in many places under a load of sewage and industrial effluent trapped between weirs and causeways, and the native fish replaced by predatory aliens.
The university’s zoology department head, Prof Nadine Strydom, said on Monday she and her third-year students had done the field survey as a follow-up to a 2014 study – and the results confirmed shocking changes.
“We returned to known points where native fish were recorded five years ago, but this time we found just two specimens of the endangered Eastern Cape redfin minnow.
“The goldie barb and Cape kurper were missing.”
There were points on the Baakens where the stench of pollution was obvious and no life was visible at all.
In Settlers Park in the lower Baakens Valley, up to 2,000 alien southern mouthbrooder were netted in the space of 15m – but not a single native fish, she said.
“It’s tragic, disrespectful of a wonderful asset and contrary to South Africa’s commitment to the international Convention on Biodiversity.”
The redfin minnows in the Baakens are some of the last members of the Mandela lineage of the species, which occurs in rivers that flow into Algoa Bay – and nowhere else in the world.
News of the NMU survey coincides with the release of a UN report warning that globally one million species are threatened with extinction because of human activity.
Strydom said the reduced flow of the Baakens – because of drought and increased development in the river catchment, which in turn meant less groundwater seepage – had exacerbated the situation.
“It’s not strong enough to flush out the pollution and get over the concrete barriers, so the water becomes anoxic because it is laden with too many nutrients.“The fish communities become increasingly isolated, and eventually die off.”During their practical, the university team measured oxygen levels of just 45% in running water where it should have been 100%.A study done in the late 1980s by fisheries expert Dr Anton Bok recommended that fish ladders should be installed to help the native fish to move over the five causeways and two high weirs in the bottom 15km of the 23km river.Besides the native freshwater species, this intervention would enable the migration of marine species like Cape moonies, gobies and mullet which needed to swim upriver and feed on insect larvae in the water during their juvenile phase, Strydom said.“But there are still no fish ladders, so an entire ecosystem has been cut off.”Populations of aggressive alien fish like banded tilapia and southern mouthbrooder preyed on the native minnows and competed with them for scarce resources, she said.“These alien fishes are popular with members of the public, who released unwanted stock into the river at some point – triggering and now fuelling their expansion.“We are on the brink of a local extinction on our watch in our backyard.“If it happens we don’t know exactly what the repercussions will be, but we do know that the Baakens, so important to our metro, is small and very susceptible to change.”She said the native fish of the Baakens River were as important as charismatic animals like rhino and elephant.They were an asset for the metro and if they could be protected they could be showcased to tourists.“As the most urgent intervention, we need to do an audit of all waste water running into the Baakens.”Conservationist Sue Spies, from the Port Elizabeth chapter of the movement Extinction Rebellion, said the impending destruction of a neighbourhood species should ring an alarm bell.