Introductions of Aquatic Organisms in Africa

B. P. Satia1 and D. M. Bartley2

1 Policy and Planning Division

Fishery Resources Division2

 

Introduction

Introductions and transfers (briefly introductions1) of aquatic organisms into and out of Africa are an old practice. Compared to other continents, the phenomenon is recent, approximately 150 years old. This time factor may, however, be a reflection of the absence of records. There are few major rivers and lakes in Africa which have not been subjected to deliberate or inadvertent introductions.

In the early 1980's FAO started a database on international introductions of inland aquatic fishes (Welcomme, 1988). Recently, this database has been expanded, through an internationally distributed questionnaire and a literature search, to include marine organisms and other aquatic taxa, such as molluscs and crustaceans (Bartley and Subasinghe, 1996). Coverage in the database is still uneven, probably being most complete for freshwater fish and least complete for aquatic plants. Although some introductions that have resulted from ballast water and fouling organisms are included in the database, no effort has been made to consider these inadvertent introductions in this article.

The information presented in this article is derived from the FAO database. The data base indicates that over 2,800 introductions have been made world-wide. Of these, 430 introductions were made into Africa; about 30 out of Africa and about 140 among African countries.

These introductions reflect prevailing attitudes and values by the public and private sectors in which the primary concern is socio-economic benefit. There is very little evidence that conservation, protection and long term sustainable use of biodiversity by humans were central considerations.

1 Introduced species (includes both non-indigenous and exotic species): Any species intentionally or uccidentally transported and released by humans into an environment outside its present range.

Transferred species (includes transplanted species): Any species intentionally or accidentally transported and released within its present range.

Species Introductions

One hundred and thirty-nine (139) species from 87 genera and from 46 families have been introduced into 42 African countries. The majority (79%) of the introduced organisms are finfish, with relatively few molluscs (7%) and crustaceans (9%). The five most often introduced species were common carp (28 records), rainbow trout (19), large mouth bass (19), Nile tilapia (17) and grass carp (15). Thus, about 4 % of the species account for 23% of the introductions. By family, the most often introduced were Cichlidae (116 records), Cyprinidae (81), Centrarchidae (50) and Salmonidae (40). About 9% of the families account for 67% of the introductions. The large and varied number of species from tropical to temperate environments implies efforts to exploit almost all the aquacultural zones of the continent.

Three main waves of introductions are identified: before 1949 (93 records); 1950-1989 (226) and after 1990 (22 records). There are also 77 introductions of unknown dates. Figure 1 shows introductions by decade. The relatively high number of introductions between 1950-1959 (78) and 1960-69 (60) is a reflection of the search for the "appropriate" species for aquaculture development, for the stocking of

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Figure 1. Chronology of introductions - Africa

(Note that introductions out of African countries could be into other African countries; introductions into African countries could be from other African countries as well.)

 

man-made lakes and for the control of disease vectors and weeds. The subsequent reduction per decade after 1980 is apparently related to the growing awareness of the possible negative effects of species introductions and to legislation, particularly in developed countries prohibiting such introductions.

Africa has received introductions from all continents except Oceania and Antarctica. The source of parent stock seems to have been linked to "colonial affinities". At the same time, Africa has also given to the other continents. The most remarkable of these exports was the Nile tilapia (Oreochromis niloticus) from four countries (Ghana, Egypt, Kenya and Senegal) to the Philippines. This parent material has been improved genetically by ICLARM researchers under the Genetic Improvement of Farmed Tilapia (GIFT) Project, to become what is known as the "super tilapia" (Eknath et al., 1993).

There have also been about 140 intra-African introductions of species. The intensities of introductions, that is, the number of introductions into and out of a country, for the ten countries that have had the most introductions is summarized in Table 1.

Table 1. Intensities of introductions for 10 principal countries

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Reasons for the Introductions

In many developed countries, species are often introduced to freshwater bodies to create sport fisheries. In most African countries, introductions have been made to produce high quality fish protein, alleviate poverty and hunger, as well as provide employment, control disease vectors and weeds. In the FAO data base, these different purposes have been grouped into three main classes: Aquaculture development, biological control and capture and sports fisheries. Figure 2 presents a classification of introductions into Africa according to purpose of introduction. Besides the purpose categories mentioned above, there were five reported cases of accidents, 10 cases of natural migration to the wild and eight introductions to fill so called " vacant niches". There were also 71 introductions with unknown motivation.

Status and Impact of the Introductions

The impacts of these introductions are summarized in Table 2. The objectives of some introductions could not be met and several species (34%) have become widespread in both rivers and lakes. In a few cases, succes has followed the introductions of species as a foundation for capture fisheries. This has been the case with the introduction of the voracious Nile perch (Lates niloticus) into Lake Victoria. This predatory species is reported to have contributed to the elimination of over 300 species of haplochromine cichlids and changed the primarily small-scale artisanal fishery on the lake into a multi-million dollar commercial fishery that supports industrialized processing and export ventures (Pitcher and Bundy 1996; Mann, 1970; Ogutu Ohwayo 1990).

Another example is the introduction of the pelagic clupeid Limnothrissa Miodon into Lakes Kivu and Kariba and its accidental diffusion downstream to Lake Cahora Bassa, leading to the establishment of substantial stocks of fish that have formed the basis of important Kapenta/Sardine fisheries in these lakes and reservoir. The sardines have, however, altered the zooplankton composition and possibly other elements of the ecosystem (Marshall 1991; Mayabe 1987; Jackson 1960). Yet a third important fishery that has been established through introductions is the Heterotis niloticus fishery on the Nyong River in Cameroon (Depiere and Vivien, 1977).

In the three cases cited, the current fishery has increased fish supplies two to three fold and helped maintain a high per capita fish consumption in the face of significant increases in human population. However, these changes have also introduced a series of socio-economic problems from deforestation to provide fuelwood for processing to a shift in the rural economy of the locality (Depiere and Vivien, 1977; Reynold and Greboval, 1989).

With regard to aquaculture species, Cyprinus carpio has be

come well established in many countries but the Oreochromis spp. remain the principal aquaculture species. It is reported (Lazard, 1990 ) that the introduction of Oreochromis niloticus into Côte d'Ivoire has led to a significant development of fish culture in the country. It is really a paradox, that while Africa was/is scouting for a suitable fish species to be introduced for aquaculture, the potential of Oreochromis niloticus was recognized and acted upon outside the continent. China and other Asian countries now dominate a rapidly increasing global production through aquaculture, while the first major genetic improvement of the species was first reported in the Philippines.

 

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Figure 2. Purpose of introductions - Africa

Regrettably, very few broad spectrum analysese that take into account ecological as well as socio-economic parameters have been done on the introductions in Africa (Bartley, 1993; Reinthal, 1993; Coates, 1995). Where analysis have been undertaken (Lake Victoria and River Nyong) it is reported that the fish fauna has been drastically altered; native species have been eliminated; the situation is virtually irreversible and the introduced fauna is established and cannot be removed easily in economic or practical terms. Ogutu-Ohwayo and Hecky (1990) report, however, that while the introduction of L. miodon into Lake Kivu and Kariba reservoir has established highly successful fisheries, the effect on the pre-existing fish community or trophic ecology is very small.

It is important to note also that the effects of introductions could take a long time to manifest themselves. In the three flourishing fisheries cited in this study, the time frame was 15 to 20 years. In general terms, the negative effects of introductions include the degradation of the host

Table 2. Status and impact of African introductions according to most common reasons for introductions

environment, the disruption of the host community through competition and displacement, stunting and predation as well as nuisance to the fisheries (Leveque and Quensiere 1988, Ogutu, Ohwago and Hecky 1990, Moreau et al 1988).

In view of the potential harmful impacts of introduction, and recognizing the necessity, in the interest of present and future generations of humans, to protect the environment and its biota from any potential negative impacts, fisheries professional societies, governments, intergovernmental organizations, non-governmental organizations, etc. have contributed to the enactment/adoption of regulations, biosafety protocols and codes of practice on the responsible use of exotic species (FAO 1995a, 1995b; Pullin 1994). Foremost in this regard are the ICES/EIFAC Codes of Practices and Manual of Procedures for Consideration of Introductions and Transfers of Marine and Freshwater Organisms (Turner, 1988). This code has been adopted by the Committee for Inland Fisheries in Africa (CIFA).

These instruments emphasize a precautionary approach to species introductions in order to reduce the risk of adverse impacts, to establish corrective or mitigating procedures in advance of actual adverse effects, and to minimize unintended introductions to wild ecosystems and associated capture fisheries (FAO 1997).

Conclusion

Africa faces a major challenge. There is, on the one hand, public outcry at the undesirable ecological consequences of some introductions and, on the other hand, there is the undeniable and significant contribution of some introductions to much needed food fish supplies. The challenge (which is not limited to Africa alone) is to work out strategies that balance the need to address hunger and poverty and the sustainable use of natural resources and ecosystems.

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