The largemouth bass is a carnivorous freshwater fish native to North America. The largest species of black bass, it is highly prized among anglers, though it is also quite infamously invasive outside of its native range.
“In the park, we don't have a big problem with large mouth or any of the bass species, but in South Africa in general, they are a bit of a problem. They are everywhere, actually,” said Dumisani Khosa, a freshwater ecologist at Kruger National Park, who explains the history of invasions in South Africa by American bass.
“Largemouth bass was introduced in 1928, and then you have the smallmouth bass which was introduced in 1937 and then later on, we have the spotted bass which was introduced in 1939 and then Florida bass in the 1980s,” said Khosa.
He explains that these introductions were mostly part of a government-backed plan to expand recreational angling opportunities in the country. However, these species are not native here.
“They have different life history strategies that our native species are not adapted to, or they are not used to, and remember they are predators,” he said.
To complicate things, they're top predators in many systems, with little to no competition and a penchant for spreading.
“We did one survey in 2016 where we went to the Breede River. And we sampled the Breede River from the source up to the sea or the estuaries. There were bass found in each and every section of the river,” said Khosa.
He further explains that this trend is common across the country, with no sign of stopping. Partly because of how difficult these bass are to remove.
“The research that we have done… it shows that it is practically impossible to remove bass once they establish in the river system,” he said.
In the short term this means localized extinctions, but in the long term this could mean disruptions to whole freshwater ecosystems.
“We're looking at changes in habitat structure. We're looking at a lot of different trophic levels, and this is having a huge impact on that,” said Khosa.
Though he is concerned, through consistent monitoring he has found that ecosystem resilience can be a major deterrence to the bass invasion.
“If you have a resilient system, like you have a good functional diversity, where all the niches are filled, then you will have a good system that is more stable or resilient to some sort of invasion or any sort of disturbance,” said Khosa.
The rivers of Kruger National Park, for example, have not yet been invaded. Khosa believes this has to do with the high biodiversity within the park and the collaboration between scientists, researchers, and even other countries.
“At the end of the day, it’s about making sure that there is collaboration between the different countries, because rivers know no boundaries,” he said.
Whatever happens at a river’s source impacts everyone downstream. A lesson just as relevant in Utah as South Africa.
