The Invasive Species Problem
Increasingly, global trade and communication are directly contributing to the mixing of faunas and floras across biogeographical boundaries. To describe this new epoch of widespread anthropogenic influence, some researchers have suggested the term Homogocene. Species suddenly taken to new environments may fail to survive but often they thrive, and they become invasive. This process, together with habitat destruction, has been a major cause of extinction of native species throughout the world in the past few hundred years. Although in the past many of these losses have gone unrecorded, today, there is an increasing realisation of the ecological costs of biological invasion in terms of irretrievable loss of native biodiversity. Invasive species are organisms (usually transported by humans) which successfully establish themselves in, and then overcome, otherwise intact, pre-existing native ecosystems. Biologists are still trying to characterise this capability to invade in the hope that incipient invasions can be predicted and stopped. Factors may include: an organism has been relieved of the pressures of predators or parasites of its native country; being biologically "hardy", for example, has short generations and a generalist diet; arriving in an ecosystem already disturbed by humans or some other factor. But whatever the causes, the consequences of such invasions - including alteration of habitat and disruption of natural ecosystem processes - are often catastrophic for native species.
The Common Carp
Cyprinus carpio (the Common Carp) has been nominated as among 100 of the "World's Worst" invaders. The common carp (Cyprinus carpio) has been introduced as a food and ornamental fish into temperate freshwaters throughout the world. It is considered a pest because of its abundance and its tendency to reduce water clarity and destroy and uproot the aquatic vegetation used as habitat by a variety of species.
The feeding habits of the common carp (Cyprinus carpio) where they are constantly stirring up the substrate, mean that they can greatly increase the turbidity of the water (NIWA, 2003). This makes waterways unattractive, reduces the abundance of aquatic plants, and can render the water unsuitable for swimming or drinking even by livestock, (NIWA, 2003). This feeding behaviour also destroys rooted aquatic plants that provide habitat for native fish species and food for waterfowl (Dentler 1993). Experiments showed that carp increased turbidity through the resuspension of bottom sediments, caused the loss of macrophyte cover due to low water clarity and uprooting, and released phosphorus normally locked up within bottom sediments and aquatic macrophytes. They also lowered the abundance of macroinvertebrates by predation and loss of habitat. (Parkos & Wahl, 2000) Bellrichard (1996) found that alterations in macrophyte biomass are due to direct effects of common carp. In their review of literature, Richardson et al. (1995) concluded that common carp has had noted adverse effects on biological systems including destruction of vegetated breeding habitats used by both fish and birds. Cyprinus carpio has been introduced to over 140 countries, 18 of which reported adverse ecological impacts, (Casal, pers.comm., March 7 2003). Common carps are active swimmers that can leap obstacles up to 1 metre high and negotiate torrential flows (Ref. 2906, in FishBase, 2003). Carp can typically be found in small schools, although larger carp often lead a solitary existence (Smith, 1991. In Chumchal, 2002). Source: http://www.issg.org/#Invasives
The SA Carp Society recognises the facts brought forward by the ISSG. We do, however, believe that carp form an integral part of the South African ecology and that no reason exist for the eradication of the species. Carp have been introduced in South Africa more than 300 years ago. Since then indigenous species have learnt to co-exist with carp, without the adverse affects being experienced in other countries. Carp has become a natural food source for humans and a variety of indigenous species, which include the Sharptooth Catfish, Yellow Fish and various other species of fish and animals. In South Africa, factors like habitat destruction, pollution and bad water management have much bigger impacts on habitat and indigenous fish species. Fact: It would be too expensive to eradicate carp from our waters and even then it would be impossible as it would re-populate the waters in a short period of time.
Fact: It was therefore accepted that no drastic measures would be brought forward to implement total eradication of the species in South Africa. There is, however, still a lot of negative sentiment towards carp for being alien. The SA Carp Society is committed to change negative perceptions about carp. Our mission has always been to promote respect towards other facets of angling and other types of sport. Our policy as sportsmen must be: Respect me and I will do the same. We call on all other facets of fishing to abide by this basic rule.