Come fish with me
In a biological context, the term ‘alien’ refers to organisms that have been introduced into South Africa from outside our country.
Therefore, alien fish are all fish that have not naturally evolved in our rivers.
The main reasons for introducing alien fishes into a country are for the pet trade and for angling. The first alien fish in South Africa were goldfish imported into Cape Town in 1726.
The second was brown trout that were imported to provide opportunities for flyfishing. These were followed by many more introductions and today the pet trade imports more than 200 species of fish into the country and alien bass, carp and trout are the focus of a vibrant sport fishery.
Sport fishing and the pet trade are important economic activities that provide employment in the retail and service industries. In addition, angling is an important recreational activity for many South Africans.
While there are many alien fishes that never escape from captivity, some establish populations in the wild either after being intentionally introduced or when they escape from captivity. When these alien fish spread from their point of introduction and impact negatively on the recipient ecosystem, they are termed ‘alien invasive species’. There is little doubt that aggressive fish such as bass and trout that prey on native fishes, frogs and insects can have major impacts on these communities.
In the Eastern Cape for example, the Eastern Cape Redfin and the Border Barb did not evolve with aggressive hunters such as bass and trout. They are ill equipped to evade these predators and, as a result these endemic fishes have been wiped out of streams that have been invaded. These target fishes have very limited distributions. The Eastern Cape Redfin for example, occurs only in the Baakens, Sundays and Swartkops Rivers. As a result of habitat degradation and the impact of alien fishes in the lower reaches of these rivers, the Eastern Cape Redfin is now only found in small sections of headwater tributaries.
Similarly, the remaining populations of the Border Barb now occur only in small sections of the Keiskamma and Buffalo Rivers, where they are squashed between troutinvaded headwaters and the degraded lower reaches of the river. As these fishes occur nowhere else on earth, preventing the invasion of their last refuges by alien predatory fishes is a high conservation priority.
Some alien invasive species provide economic benefits and recreational pleasure, but also cause grave environmental harm.
Controlling the spread of these species has resulted in considerable conflict between conservation authorities and anglers. Managing such “con- flict species” therefore requires the development of approaches that maximise the social and economic contributions of alien sport fishes while mitigating against further spread and impacts. In this regard, the South African Institute for Aquatic Biodiversity (SAIAB) has been supporting the Department of Environmental Affairs in developing national legislation for the management of alien fishes. This legislation seeks to develop an area-based approach which facilitates the use of alien fishes in areas where they already occur and where they have limited impact on conservation priority species; and to prevent their spread into areas where they are likely to cause harm to indigenous species.
My research group has developed an interactive fishing game to raise awareness about alien invasive fishes and their impact on native species. Come and play the game at WaterWorld during Scifest.
• Prof. Olaf Weyl is Principal Scientist at NRF-SAIAB. His current research focus at SAIAB is geared towards providing information with which to better manage Africa’s aquatic biodiversity.
See: http://www.saiab.ac.za/ professor-olaf-weyl.htm or follow Olaf's research at SAIAB on Facebook; and http://www. saiab.ac.za/
or contact Penny Haworth, Manager: Communications and Governance. saiab@saiab.ac.za; Tel: +27 (0)46 603 5812.