Applying standardised methods to assess the potential risks of alien freshwater crayfish introductions to South Africa

Abstract

Alien freshwater crayfish have been widely introduced worldwide for aquaculture and the pet trade. Despite providing societal benefits, crayfish introductions are also known to cause adverse impacts in areas of introduction. This study used the recently developed Risk Analysis for Alien Taxa (RAAT) framework to assess the risk associated with 14 alien freshwater crayfish introductions in South Africa. Thirteen of the 14 species were assessed as high risk because they are likely to be introduced to South Africa and have the potential to cause major environmental impacts. Eight of these species are listed under the South African National Environmental Management: Biodiversity Act (NEM: BA) Alien and Invasive Species (A&IS) Regulations, which implies there is an obligation to manage them. This notion was supported by the recommendations from the risk analyses for Cherax cainii, C. tenuimanus, and C. quadricarinatus. The two marron species (C. cainii and C. tenuimanus) have no known naturalised populations and are likely confined to aquaculture facilities. Cherax quadricarinatus is already widespread and control methods should focus on minimising spread, as eradication is no longer feasible. The recommendations from some of the risk analyses do not agree with the current listing under the A&IS Regulations. Procambarus clarkii is already known to be invasive but is not listed and there is anecdotal evidence that C. destructor, Faxonius limosus, F. rusticus, Pacifastacus leniusculus, and Pontastacus leptodactylus are present in the pet trade and their presence needs to be verified. Crayfish can become conflict-generating alien species because they have both major negative impacts and socio-economic benefits. Therefore, the recommended management options aim to preserve benefits while limiting negative impacts by restricting the importation of high-risk species for new introductions and implementing interventions to prevent spread and minimise impacts for established introductions.