News » A Review of Freshwater Crayfish Introductions in Africa

A Review of Freshwater Crayfish Introductions in Africa

By: Takudzwa Comfort Madzivanzira (SAIAB PhD student)

Non-native species are widely believed to be one of the most common drivers of biodiversity loss in many natural habitats. Among many non-native species are numerous freshwater crayfish species which have been spread beyond their indigenous ranges by humans. Freshwater crayfish species exhibit broad tolerances to a wide range of environmental conditions because they grow big, breed profusely, are found in large numbers and eat almost anything means that they can survive in a variety of habitats around the world. Crayfish introductions have not spared the African continent, which, apart from Madagascar, has its own native crayfish species, is naturally devoid of native freshwater crayfish.

Crayfish invasions have been well studied around the world, but less so in Africa. Therefore, this research set out to compile up to date information on crayfish introductions on the African continent, to better understand the reasons and pathways that have driven these introductions, improve the understanding of the nature and magnitude of the environmental impacts they have generated, and identify knowledge gaps to better prioritise their management and ultimately, avoid further introductions. The research team analysed crayfish introductions in Africa. The literature they reviewed showed evidence of the introduction of nine non-native crayfish species in fifteen countries on the continent, with five of these having established naturalised populations in the wild (see map for established species).


Introduction routes of crayfish species into Africa and introduction locations within the continent.
Dashed lines show translocations within the African continent whilst continuous lines show
introductions from outside the continent (Source of map: Madzivanzira et al. 2020).

Crayfish were introduced into Africa as a way to address poverty and hunger, but there is not much evidence of success. The establishment of wild crayfish populations in Africa’s freshwater systems is a cause for concern as crayfish are known to affect aquatic plants, aquatic insects, frogs, fish and their eggs. In Africa, crayfish are linked to damage in agricultural water infrastructure, damage to fishing nets and declining fisheries performance, which all affect human livelihoods. Not much has been documented about their impacts on other organisms in African freshwater systems which is a knowledge gap on the continent.

Study Outcomes

This study, undertaken by the Freshwater Research Team at SAIAB, showed how difficult it is to prevent crayfish introductions. In the event of a failure to prevent crayfish from arriving in respective countries, the researchers suggest methods such as early detection, rapid response, monitoring programmes and citizen science, which are all critical elements for environmental managers to control or suppress crayfish populations so that they can minimise associated impacts. This will help to ensure that people continue to benefit from the ecosystem services offered by freshwater systems to sustain their livelihoods.

To increase the success of management interventions, this study suggests that traditional crayfish control methods need to develop and incorporate novel control techniques. Furthermore, the study revealed that literature on the ecological impacts of crayfish on the African continent is scant. This constrains conservation efforts since there is not enough evidence to compel policy makers to prohibit further crayfish introductions.

Investigating the impacts of freshwater crayfish species and monitoring the extent of their spread should be prioritised, as these invaders have the potential to affect important African ecosystems on the continent such as Lake Malawi, Lake Victoria and the Okavango Delta, among others.

    
Image 1                                                                          Image 2

 Captions: 

Image 1: The Louisiana red swamp crayfish (Procambarus clarkii) is one of the species which is spreading at a fast rate on the continent. This species was collected from Mimosa Dam in the Free State Province of South Africa and kept in a controlled room at SAIAB for experiments. (Photo: TC Madzivanzira)

Image 2: The Australian redclaw crayfish (Cherax quadricarinatus) is one of the species which is spreading at a fast rate in Southern Africa. This species was collected from Lake Kariba in Mashonaland West Province of Zimbabwe. (Photo: TC Madzivanzira)

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This research was published in Reviews in Fisheries Science and Aquaculture journal cited as: Madzivanzira TC, South J, Wood L, Nunes AL and Weyl OLF (2020). A review of freshwater crayfish introductions in Africa. Reviews in Fisheries and Aquaculture. https://doi.org/10.1080/23308249.2020.1802405.

The study forms part of Takudzwa Madzivanzira’s PhD research project supported by the National Research Foundation (NRF) South African Research Chairs Initiative of the Department of Science and Innovation (DSI) (Inland Fisheries and Freshwater Ecology, Grant No. 110507). The research is also supported by the World Wide Fund (WWF) for Nature Upper Zambezi Programme funded by DOB Ecology.

Takudzwa Madzivanzira is supervised by SAIAB Chief Scientist, Professor Olaf Weyl and SAIAB Postdoctoral Researcher, Doctor Josie South.