Spatio-temporal patterns of fish assemblages in coastal West African rivers: a self-organizing map approach

Abstract

We investigated spatio-temporal patterns of fish assemblages in four small coastal rivers in SouthEast Ivory Coast. The samples were collected between July 2003 and March 2005 at 8 sampling sites (2 per river: 1 upstream and 1 downstream). A total of 59 fish species belonging to 39 genera, 23 families and 11 orders were captured. Perciforms (30% of the families and 33% of the species), followed by Siluriforms (22% and 22%), Osteoglossiforms (13% and 17%), Characiforms (9% and 10%) and Pleuronectiforms (9% and 3%) were the most abundant orders. Among the families sampled, Cichlidae (20% of the species), Mormyridae (13%), Clariidae (10%), Cyprinidae (10%) and Characidae (8%) were largely represented. Among the 59 fish species captured, we identified fifteen marine/brackish species and two introduced species. To analyse patterns of fish assemblages, we used a non-linear clustering technique, the self-organizing map (SOM). Using SOM, samples were classified into 4 clusters, mainly related to the spatial location of the sampling sites. Except for the distance from the source of the river, environmental variables (width, depth, current velocity) did not show a clear distribution gradient on the SOM map. This pattern was explained by the abundance of estuarine/marine species (i.e. 25% of the species) characterizing the lower course of the rivers studied. Such a distribution of estuarine/marine species colonizing the lower and middle course of the rivers was explained by the absence of dams and contrasts with the patterns observed in more fragmented rivers of Ivory Coast. Therefore, we suggest that these small streams should be preserved in order to permit estuarine/marine species to migrate between streams and the Aby lagoon, thus allowing their large distribution and their reproduction in favourable habitats. We suggest particular attention be given to the Soumié River basin which represents the only preserved stream ecosystem within the Bia River basin. Key words: ichthyofauna / coastal rivers / hierarchical clustering / self-organizing map / Western Africa Résumé-Distribution spatio-temporelle des assemblages de poissons des cours d'eau de la côte ouest africaine : une approche basée sur les cartes de Kohonen. Nous étudions les types de distribution spatio-temporelles d'assemblages de poissons de quatre cours d'eau du sud-est de la Côte d'Ivoire. Les échantillonnages de 8 sites (2 sites par rivière : un amont et un aval) sont effectués entre juillet 2003 et mars 2005. Au total, 59 espèces de poisson appartenant à 39 genres, 23 familles et 11 ordres sont capturées. Les Perciformes sont les plus abondants (30 % des familles et 33 % des espèces), suivis des Siluriformes (22 % des familles), des Ostéoglossiformes (13 % et 17 %), des Characiformes (9 % et 10 %) et des Pleuronectiformes (9 % et 3 %). Les familles les plus largement représentées sont les Cichlidés (20 % des espèces), Mormyridés (13 %), Clariidés (10 %), Cyprinidés (10 %) et les Characidés (8 %). Des 59 espèces de poissons capturés, quinze espèces de milieu ...

Reproductive biology ofChromidotilapia guntheri(Sauvage, 1882) (Cichlidae, Perciformes) in four coastal rivers (Ehania, Noé, Soumié and Eholié) of Côte d’Ivoire in West Africa

“…The four small coastal rivers (Soumié, Eholié, Ehania and Noé) studied belong to the Western Guinean ichthyoregion, sector Eburnéo-Ghanaian, and are located in lowland rainforest (Daget and Iltis, 1965 (Figure 1) (Konan et al, 2006). In each river, two sampling sites were retained: upstream and downstream.…”

“…Soumié River, Eholié River, Ehania River, Noé River (Konan et al, 2006). 1 = first sampling site, 2 = second sampling site.…”

“…Despite its widespread occurrence, C. guntheri has never been adequately studied. Studies on this species are scarce and available information is on the species distribution in natural habitats (Teugels et al, 1988;Lévêque et al, 1991;Vivien, 1991;Paugy et al, 1994;Konan et al, 2006). Although it is not an economically important species, it does form an important component of the subsistence catch in Ivorian coastal rivers (Gourène et al, 1999;Da Costa et al, 2000;Konan et al, 2006).…”

“…Studies on this species are scarce and available information is on the species distribution in natural habitats (Teugels et al, 1988;Lévêque et al, 1991;Vivien, 1991;Paugy et al, 1994;Konan et al, 2006). Although it is not an economically important species, it does form an important component of the subsistence catch in Ivorian coastal rivers (Gourène et al, 1999;Da Costa et al, 2000;Konan et al, 2006). It is therefore important to know its reproductive biology and spawning behavior so as to ensure its conservation as well as its full utilization as a sustainable resource.…”

Structure of endemic fish assemblages in the upper Yangtze River Basin

“…In fish ecology, the structure of fish assemblages depends on many interacting factors and can be quantified by summarizing species richness, composition and feeding guilds (Karr, 1981). Classification of sites (or areas) based on fish species assemblages has been elaborated for many lotic systems (Konan et al, 2006;Park et al, 2006;Kruk et al, 2007;Lasne et al, 2007). Modelling the composition of fish assemblages on the basis of biotic and abiotic environmental descriptors is an important aspect of the management of aquatic ecosystems.…”