Lowveld ecosystem under threat of crayfish
People are encouraged to destroy the redclaw crayfish when they find them, or eat it, but to stop moving them around as they are detrimental to the ecosystems and water resources.
Just as redclaw crayfish have become a major marine problem globally, this invasive species have now also found their way into the Lowveld’s waters by way of the Komati and Crocodile rivers.
According to Prof Gordon O’Brien, senior lecturer of the School of Biology and Environmental Sciences at the University of Mpumalanga, this species, which can grow up to 30cm, should be destroyed as they are detrimental to the ecosystems and water resources.
“They were introduced into the Inkomati Catchment Water Treatment from eSwatini as an aquaculture project to breed crayfish, but it did not work. They have now escaped and moved from the Komati River to the Crocodile River in Mozambique.” O’Brien explained that the biggest problems with this incomplete indigenous species crayfish are that they are competitors to natural species, reproduce en masse and grow relatively quickly to sizes as big as 30cm each. Other species, such as prawns, crabs and fish, are negatively impacted by the redclaws. Marine biologists are worried that they will in future pose an even greater threat to regional rivers.
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“We are currently dealing with too much water being pumped into our rivers, leading to water quality contamination and pollution. This could see crayfish invasion worsen in the area,” he said. He also said crayfish are moved by people for many reasons; some by accident, and some collect them in cans to look at them because they think they are pretty. However, they often escape. O’Brien explained that some anglers deliberately move crayfish around as they wrongly believe it would lure black bass fish, a favourite catch of theirs.
“The actual fact is that the crayfish eat the eggs or attack the breeding nests of the bass, which in turn eat the crayfish, not because it is considered food, but to prevent them from eating their babies. This has now led to certain members of the public thinking that crayfish are harmful and negatively impact the bass population. The problem is that these redclaws are moving around Mpumalanga’s rivers and into the nearest provinces. It is a big problem to remove them from rivers, but we encourage people that when they find them, to destroy them; should they eat them, they must do so, but not move them around,” O’Brien urged.
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According to SANParks’ Dr Dumisani Khosa, a freshwater ecology expert, crayfish invasions are a serious conservation and management concern as they negatively impact aquatic biota, including fish, crabs and both invertebrate and macrophyte biodiversity. Invasive macrophyte species such as redclaw crayfish may modify habitat structure and thus influence associated organisms.
“Following this 2016 discovery, crayfish invasion was recognised as a major threat to the functioning of KNP’s rivers, requiring careful monitoring and control. Almost seven years later, in May 2023, we set crayfish traps in the Crocodile River at Crocodile Bridge, approximately 50km downstream of the Van Graan Dam, to establish how far crayfish had dispersed. Three redclaw crayfish were captured, suggesting a downstream spread of about 7km per year,” he said.
Redclaw crayfish consume high numbers of fish food and plant material, regardless of temperature, in comparison to native crabs. They also negatively affect fisheries through scavenging. They pose a significant threat to the park’s ecosystem, due to several factors such as being voracious omnivores that consume large amounts of fish, invertebrates and plant material, disrupting the natural food chain, which can negatively impact native species.
