SEARCHING FOR SANDFISH IN THE TANKWA KAROO

Dr Oliver Cowan, Conservation Scientist, EWT Conservation Science Unit
OliverC@ewt.org.za

An important part of the EWT Conservation Science Unit’s (CSU) project to map and model the distribution of animal species of conservation concern in South Africa is to fill key knowledge gaps. These gaps are identified after consultations with taxon-specific experts – an example of this is a workshop we held with freshwater fish experts from CapeNature and the Freshwater Research Centre (FRC) last year. A key outcome of this workshop was the potential for new populations of the Clanwilliam Sandfish to be found in the relatively unexplored Tankwa River.

Historically, the Sandfish was widespread throughout the Olifants-Doring River System but sadly, like many of our endemic freshwater fishes, it is now Endangered. Sandfish populations have been decimated by the introduction of predatory alien fish, such as bass, and changes to river flow. These reduced numbers are currently fragmented within the Doring River and its tributaries with potentially only a single viable, growing population remaining.

The neighbouring Tankwa River was previously not considered viable habitat as it is non-perennial, drying up during the hot summer months. However, scientists at the FRC had noted on satellite imagery what appeared to be permanent pools dotted along the otherwise dry riverbed. They thought the pools may provide refugia for Sandfish, a haven from the dangers rampant throughout the catchment. Armed with this information, researchers from the CSU and the FRC set out to hunt for Sandfish in the Tankwa in December 2019.

As one drives out of Ceres, one quickly says goodbye to cell signal and tarred roads. The Tankwa at this time of year is a harsh environment and it did not help that it was in the midst of a record-breaking drought. We had been warned, when applying for research permits, of the situation but were unprepared for the sight that met us at Oudebaaskraal Dam in the Tankwa Karoo National Park. What had once been the largest dam in the region was now bone-dry, flamingos replaced by the occasional dust-devil.

Somewhat chastened, we spent the next few days trekking around the semi-desert, attempting to locate the pools we had previously identified in air-conditioned offices back in Cape Town. With just GPS coordinates, bakkies and our feet this was no easy task, made more challenging by 40°C temperatures and an inhospitable landscape. After many false dawns we finally got lucky. Water! And water deep enough to be suitable for fish. It appeared the satellite imagery had not deceived us – in certain places, where the bedrock was exposed – groundwater pooled at the surface.

We started off with active searching: trawling our Seine nets through the pools, hoping to snare the elusive Sandfish but with no success. We found plenty of life in the form of hordes of Common Plattanas, their tadpoles, and a few freshwater crabs, but no fish. However, we weren’t too perturbed as this sampling method is imperfect – our hopes were pinned on our Fyke nets. These nets are more reliable as their set-up allows for passive capture throughout the night, extensive wings channelling fish towards concentric ring-nets from which there is no escape. The nets are quite technical to set up and require the use of the dinghy so our decision to manually inflate our aquatic steed on the first day was not in vain. We departed, optimistic about what the next day had in store.

The next morning, we were in for a rude awakening. Firstly, our precious dinghy which we had carefully placed on the bank, comforted by the knowledge that it was safe from potential thieves, was now a deflated yellow blob. Upon closer inspection, the valves revealed tell-tale teeth marks. For some reason, the plastic must have been irresistible to members of the local baboon troop, and for a moment we felt less bad about the baboon graveyard we had chanced upon earlier that week. But things were to get even worse. As we waded out to check our nets, we noticed that the final concentric ring in which we were hoping to find Sandfish was ripped and what remained was frog limbs and half-eaten tadpoles. Spoor on the riverbank confirmed our suspicions: a Cape Clawless Otter couldn’t resist the buffet he found the previous night and had swum in to gorge himself. Once satisfied, he made his escape at the expense of our net.

With tails between legs we collected what remained of our equipment and headed back to base to regroup. En route, we bumped into a farmer who bemoaned the drought, claiming that a Tankwa River tributary which once ran through his property had shrunk to a puddle. Not expecting much we went to investigate this puddle and just about convinced ourselves to drag a net through, despite its fetid appearance. Lo and behold, fish! Sure, it was not the Sandfish but rather a population of the indigenous Chubbyhead Barb, which had miraculously survived in this unlikely oasis. This species’ taxonomy is currently being revised and it is not unlikely that the DNA we extracted from this isolated sub-population proves them to be a sub-species and of substantial conservation value.

As we headed back to Cape Town later that week, we didn’t consider the trip a failure. Sure, we did not find the Sandfish despite our extensive survey, but this can allow conservation efforts to focus on the regions where it is known to occur. In addition, the miraculous discovery of the Barb population showed that wildlife continues to strive for survival despite the harsh hand that the climate (and, let’s face it, humans) have dealt it.

We would like to sincerely thank the Rand Merchant Bank Foundation for generously funding this project and our collaborators at the FRC for their assistance on this fieldtrip. To stay up-to-date with their continued work regarding the conservation of the Clanwilliam Sandfish, amongst other things, please see their website (www.frcsa.org.za) or find them on Facebook: Freshwater Research Centre.