Managing alien fish invasions in South Africa

Olaf LF Weyl


South Africa has a long history of alien fish introductions. Alien fish such as common carp, brown trout and largemouth bass were introduced because native fish faunas contained few species that had potential for fisheries development. Coupled with introductions for bio-control, aquaculture and the pet trade, alien fishes now outnumber natives in many river systems and South Africa is considered a global fish invasion hotspot. Although government mediated stocking programmes ceased in the late 1980s alien fishes continue to increase their distributional ranges through illegal private stocking, escape from aquaculture and via inter-basin water transfers. Alien fish introductions are considered one of the main threats to aquatic biodiversity because they impact on native biota through predation, habitat alteration, disease transfer and hybridisation. As is the case for other invasive biota, the control and management of alien fishes is included in the National Environmental Management: Biodiversity Act. Implementation measures include import and movement controls and, more recently, alien fish eradication in conservation priority areas. Management actions are however complicated because many alien fish are important components in recreational and subsistence fisheries that contribute towards regional economies and food security. As a result management of these conflict species often meets with considerable resistance, particularly from angling organisations. In this paper, I provide an overview of fish introductions and their associated impacts in South Africa and describe both existing and evolving national policies and legislation for the management of alien fishes. The implementation strategies used by provincial conservation authorities are discussed with regard to the available human capacity and the sometimes innovative approaches that have been used to prioritise and manage fish invasions at local levels.