4 Naga, The ICLARM Quarterly (Vol. 23, No. 4) October-December 2000 Biodiversity of Estuarine Fish Faunas in West Africa E. Baran Abstract In West Africa (between Ivory Coast and Sénégal), estuarine environments vary from lagoons to high discharge rivers to inverse hypersaline estuaries. This results in a high diversity of estuarine fish species, with an important turnover and a core of ubiquitous species. The species richness of a given estuary depends on the combination of hydrological factors (marine or freshwater dominance) and biogeography (continental biogeographic regions). The catch rate is higher in lagoons and inverse estuaries than in normal estuaries, which can be explained by the predominance of small juveniles in the latter. Clupeids are the most abundant fishes all over the region, but different systems have different dominant species. Assessing the functioning of West-African estuaries provides useful comparisons to Asian estuarine systems. Introduction In West Africa the estuarine fish fauna is an important resource for local populations. In the Southern Rivers zone for instance (Southern Sénégal - Sierra Leone), the catches of the artisanal fishery, which targets mostly estuarine-related species, amounted to 150 000 tonnes/year, and to an average of 100 tonnes/ year/km of coastline (Charles- Dominique 1994). On the other hand, the estuarine and coastal environment in this region is also subject to heavy human pressure, with an annual population growth rate of 4-7% and 60% of industries located in coastal cities (UNEP 1999). The coastal lagoons of Ivory Coast, the cities they support and the fish they produce are illustrative of the strong interaction between people and the environment. Knowledge of the estuarine fish fauna, its geographic specificities and its natural driving forces, helps in the understanding and management of this resource. This paper summarises the major trends in estuarine fish biodiversity in the region. species richness, composition and abundance of regional estuarine assemblages. This comparison pictures species rich environments, whose fauna depend both on river hydrological regimes and freshwater biogeographic regions. The focus here is on coasts covering 2 800 kilometers between Sénégal and Ivory Coast (Fig. 1). The comparison of estuarine ichthyofaunas which follows is a synthesis of several local studies compiled by Baran (1995) and Diouf (1996). Three aspects are detailed: Fig. 1. Major estuaries studied in West Africa. Sénégal Sine-Saloum Gambia Casamance Rio Buba Fatala Ebrié SENEGAL GAMBIA GUINEA GUINEA IVORY COAST LIBERIA SIERRA LEONE BISSAU ATLANTIC OCEAN 100 km Longitude (˚W) Latitude (˚N) 20 10 10 0 0 20 10 20