Aggressive, alien crayfish invade Free State dams

An invasive species of crayfish is taking over aquatic systems in the Free State, the Department of Environmental Affairs (DEA) has announced.

The red swamp crayfish (Procambarus clarkia) was discovered in a dam in the Free State Goldfields.

"It spreads all over the world – Europe, China; I think even to South America. It was probably brought in as part of aquaculture or the pet shop trade," Dr Leon Barkhuizen, aquatic scientist from the Free State Department of Economic, Small Business Development, Tourism and Environmental Affairs told News24.

Barkhuizen said that the species is damaging to the local ecosystem.

"They are extremely invasive and they are omnivorous. So far we have caught over 70; I'm busy measuring them and it's a breeding and established population."

Breeding population

The large number of juvenile crayfish suggest that it is a breeding population.

It was not yet clear how the crayfish had ended up in the province.

"We are busy with an investigation currently. At this stage it seems that it is a result of the pet shop trade," said Barkhuizen.

The DEA said that some individuals have been caught violating the National Environmental Management: Biodiversity Act, which identifies the red swamp crayfish as a Prohibited Freshwater Invertebrate.

Reports indicate that some people in the Goldfields area caught the crayfish, which can grow up to 12cm, and sold them for R10.

"This action must be stopped immediately to prevent the further spread of this highly invasive species. According to the legislation, it is an offence to be in possession of the red swamp crayfish and if a person is found to be in possession, such a person can be fined up to R10 million and/or a prison sentence upon conviction," the DEA said in a statement.

Dr Leon Barkhuizen caught this crayfish. (Dr Leon
Dr Leon Barkhuizen caught this red swamp crayfish in a Free State dam. (Dr Leon Barkhuizen)

The red swamp crayfish, also known as the Louisiana crawfish, is a carrier of the crayfish plague that devastated indigenous crayfish populations in Europe.

The US state government of Michigan highlighted its concern over the crayfish.

"Red swamp crayfish compete aggressively with native crayfish species for food and habitat. Feeding behaviour reduces the amount of available habitat for amphibians, invertebrates, and juvenile fish. Burrowing and foraging behaviour can also lead to summer cyanobacteria blooms and eutrophic conditions."

The DEA urged anyone with knowledge of where the crayfish were being sold to report the information urgently.

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