Redclaw crayfish spreading in Crocodile River in the Kruger National Park
The first invasive crayfish in the Kruger were discovered in 2016.
The redclaw crayfish is native to northern Australia and Papua New Guinea, but has been introduced around the world for aquaculture and the aquarium trade. Continental Africa has no native freshwater crayfish species, with the ecological equivalent being freshwater crabs.
However, the first record of crayfish in the Kruger National Park (KNP) was in February 2016, just below Van Graan Dam on the Crocodile River and the border of the park.
A scientist of freshwater ecology at SANParks, Dr Dumisani Khosa, said these crayfish had previously been recorded upstream of the Crocodile River, and in high abundance throughout the Komati River, including at the confluence with the Crocodile River, so it is possible that they dispersed into Kruger from there.
“Following this 2016 discovery, crayfish invasion was recognised as a major threat to the functioning of KNP 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 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.
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Khoza also said crayfish invasions are a serious conservation and management concern as they negatively impact aquatic biota, including fish, crabs and both invertebrate and macrophyte biodiversity.
Redclaw crayfish consume high numbers of fish fry and plant material, regardless of temperature, in comparison to native crabs.
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They also negatively affect fisheries through scavenging and destruction of fishing gear. In Lake Kariba, they cause losses to Zimbabwean fisheries of up to $512 352 a year.
As with many invasive species, removal from a system is highly unlikely once the species is established, and as such, preventing and slowing spread is crucial during the early stages of an invasion.
