FASCINATING new research is being done on "the other Mandela” – not our former president, but a major lineage of a small, endangered Eastern Cape fish. The redfin minnow is a wonderful little icon of our province. Although it is small and seldom seen, its existence is key, researcher Bruce Ellender, a Rhodes University icthyology department PhD candidate, explained to me.
In the headwater streams where it lives, it is an integral part of the unique indigenous system of plants and animals that exist there.
This place-specific web of life injects nutrients into the water, it minimises erosion and ensures natural water flow. And this natural flow through the headwater streams is what helps to deliver that precious clean water into the main river systems for us humans, for all our many needs.
Ellender’s study is underway under the auspices of Dr Olaf Weyl of Grahamstown’s South African Institute for Aquatic Biology (Saiab) in Grahamstown. His start point was to try to understand the ecological consequences of alien fish invasion in Eastern Cape streams. But one of the key consequences of this invasion, he has now confirmed, is that it is wiping out the redfin.
Specifically the problem is the North American smallmouth and largemouth bass, two highly aggressive fish which prey on the redfin.
The redfin grows to only about 110mm long and it eats algae and aquatic insects. Besides those distinctive scarlet fins, it is olive brown on top, creamy white underneath and it has a dark band down each flank.
Although one lineage of the species occurs in the southern Cape (in the Klein Brak-Tsitsikamma river complex) it is more dominant in the Eastern Cape. We have three lineages here: in the Krom, the Swart-Gamtoos and the Baakens-Swartkops-Sundays.
This last is called the Mandela lineage because all three rivers drain into Algoa Bay, also known as Nelson Mandela Bay.
The thinking is that the Mandela evolved at the peak of the last glacial period, 20000-odd years ago. At that time, the sea level was 130m below what it is now, which would have likely ensured that these rivers were joined.
Deep in Groendal, Ellender has been studying five different, healthy populations of the Mandela lineage. The bass were introduced into the Groendal Dam in 1935 for recreational angling, and they have spread from there. Generally, they have not managed to invade the streams, kept out either by little waterfalls or, apparently, by the steep gradient of the streams.
But they have infiltrated into the lower reaches of two streams and here the redfin has been completely wiped out. This equates to 12-35% of the Groendal refuge, which is now no-go territory for them.
Indirectly, these bass are also severely pressuring the redfin. Their presence in main streams and the river proper is strangling the natural process in which the redfin would migrate through the
With consequence, populations are becoming increasingly fragmented and more vulnerable to natural pressures like periods of severe drought. Where before die-offs would be overtaken by natural recolonisation as rain fell and redfin moved through the system, now this pressure is being exacerbated.
Today, the species faces "at very high risk of extinction in the wild”.
Besides working to remove bass from these headwater streams, general rehabilitation of waterways where the redfin lived or used to live will help, says Ellender. This is already underway through a partnership between the national and EC parks’ boards and Saiab.
The passage of some of the key waterways inbetween protected parks is also a problem and perhaps the new thinking around creating "wildlife corridors” could interface here.
Besides the good scientific reasons why we need to protect the redfin – these are the slivers of life which reveal the majesty of the whole. Take a trip to Groendal, and you’ll see what I mean.