The Cape Floral Region has the highest number of threatened indigenous fish species in its rivers for a South African region, with many of these species found nowhere else in the world. Throughout the years. these fish have had to fight for survival due to invasive fish species and degradation of their habitat.
Alien fish such as small mouth bass, rainbow trout, sharptooth catfish and carp have made their way into rivers and dams, but not by accident, and not even as the result of illegal introductions like stocking fish without permits. Dig a little deeper and you discover nature conservation in the Cape has a fishy past.
“Invasive fish species is not a problem unique to South Africa, Lesotho has a problem too: says Dean Impson, freshwater fish ecologist at CapeNature. He says the Cape region has few indigenous angling fish and with nature conservation non-existent nearly 100 years ago, the unthinkable happened.
Small- and largemouth bass, rainbow trout, sharptooth catfish and carp were introduced into rivers and dams between 1890 and 1970, solely for angling purposes. This was managed through the former Cape Division of Inland Fisheries (now known as CapeNature). Jonkershoek outside Stellenbosch had the largest fish hatching facility in Africa, and its sole mandate was to introduce fish from elsewhere to stock inland waters for angling and food.
Some changes came in the 1950s when the department changed to the Cape Department of Nature Conservation. However, with an inland fisheries division, the stocking continued. “Things were different then,” says Impson.
Small indigenous fish had completely disappeared from areas where invasive fish proliferated
“When European people arrived in the Cape and saw few large fish species. they decided to fix the problem.” Little did they realise the effect it wouId have on indigenous species. “River surveys from the late 1960s showed indigenous fish were in deep trouble.” says Impson. “They found that small indigenous fish such as redfin minnows and Cape kurper had completely disappeared from areas where invasive fish proliferated. In fact. as early as the 1920s fishery experts such as Sydney Hey realised the introduction of trout into streams saw redfin minnow and Cape kurper populations collapse through predation.”
The biggest problem is indigenous fish evolved without predatory fish. “If you swim in the Cape streams. the fish approach you. They are curious. so it is no surprise that predatory alien fish annihilated them in the clear streams of the region.” The stocking of trout continued into the 1970s, but change was on the horizon. With the publication of the first Red Data Book for fish by Dr Paul Skelton, individuals started questioning why conservation funds went towards stocking ecologically harmful aliens. The focus slowly shifted to the breeding of indigenous fish and halting the stock of alien fish in sensitive areas.
Since the 1990s, the focus has moved away from hatcheries and towards conservation of the habitat. “We need the river to look after the fish instead of putting more fish into the river.” says Impson. The problem with hatcheries is not only disease and genetics. but fish released from hatcheries are also not familiar with the local conditions of the river. While CapeNature no longer supports stocking of aliens. invasive species continue to reach rivers. “Sharptooth catfish are not indigenous to fynbos. but now occur in all our major rivers.
“They were probably illegally introduced by anglers. as no permits have been issued for such stocking.”
Impson says the Breede and Berg rivers have become inundated with catfish in the last two decades. as
a single female can produce up to 30 000 eggs.
To undo the damage of the past. rehabilitation plans are underway in many of the province’s rivers. These include control projects to deal with invasive plants that choke many of the region’s rivers and reduce dry season flows, as well as successful control projects on bass in two small rivers in the Cederberg, which are not priorities for angling.
A great deal of work lies ahead, but it is hoped improvement projects will assist indigenous species in reclaiming some of the rivers.
Written by René de Klerk
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