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Australian redclaw crayfish quickly spreading in South Africa and Swaziland

A recent study, led by C·I·B Post-doc Ana Nunes, confirms the presence of established and widespread populations of the Australian redclaw crayfish in South Africa and Swaziland. It also shows that, in 14 years, the species has spread more than 100 km away from the point of first introduction which, considering the strong impacts that alien crayfish usually have on invaded ecosystems, is extremely worrying.

The Australian redclaw crayfish, Cherax quadricarinatus, originally from Australia, was first reported in South Africa 2002, after accidentally escaping from an aquaculture farm in Swaziland. Despite initial reports of the species in Swaziland and South Africa, no systematic survey had ever been carried out to determine their distribution, spread rate and population dynamics.

The authors found that the species is now present in at least three large rivers (Komati, Mbuluzi and Usutu), two tributaries (Lomati and Mlawula rivers), as well as in several irrigation dams in Mpumalanga Province. In the Komati River, the mean spread rate was 8 km/year downstream and 4.7 km per year upstream, whereas in Swaziland estimated downstream spread rate might reach 14.6 km per year. Individuals were generally larger and heavier closer to the introduction point, which might be linked to juvenile dispersal.

While the environmental impact of the redclaw crayfish in invaded habitats has yet to be determined, the possible introduction of this species into new catchments in South Africa is a matter of extreme concern, given its potential impacts on native biota, such as disease introductions or strong competitive interactions with native freshwater crustaceans.

According to Ana Nunes, “Considering that established invasive crayfish populations are usually impossible to eradicate, the possibility of implementing management actions to control the spread of crayfish populations in the international river systems studied here should be immediately discussed and coordinated between South Africa, Swaziland and Mozambique”.

Australian redclaw crayfish caught in a trap

High numbers of Australian redclaw crayfish (Cherax quadricarinatus) caught in a trap in South Africa (Photos by Ana Nunes)




The study was published in the scientific journal PeerJ

Nunes AL, Zengeya TA, Hoffman AC, Measey GJ, Weyl OLF. (2017) Distribution and establishment of the alien Australian redclaw crayfish, Cherax quadricarinatus, in South Africa and Swaziland. PeerJ 5:e3135 https://doi.org/10.7717/peerj.3135

For more information, contact Ana Nunes at ananunes@sun.ac.za