Fish distribution in relation to environmental characteristics in the Aby-Tendo-Ehy lagoon system (Southeastern Cte dIvoire)

Abstract

Although West African lagoons are known to provide significant fishery resources to populations, few studies have been done on processes responsible for their fish composition, abundance and spatial distribution. The aim of this study was to assess fish species distribution along the Aby-Tendo-Ehy lagoon system in Côte d’Ivoire. Sampling sites were distributed in the lagoon and grouped into three zones from a freshwater zone with high contributions of freshwater (zone 1) to a mixo-eurihaline water zone (zone 3), with a transition site (zone 2) located between the first two zones. Environmental characteristics showed gradual decrease of mean pH from zone 1 to 3, whereas mean conductivity, total dissolved solids and transparency measurements increased from zone 1 to 3. Salinity data were 0 all along the sampling period in zones 1 and 2 and increased up to 3 ppt in zone 3. A total of 67 species belonging to 29 families were caught. Overall fish diversity decreased from zone 1 (n=58) to 3 (n=40), with 45 species caught in zone 2. The number of species in different fish trophic categories (invertivorous, herbivorous, piscivorous and omnivorous species) decreased from the zone 1 to 3. Fish compositions in zones 1 and 2 were dominated by freshwater species, while in the zone 3 it was dominated by estuarine dependent species. The canonical correspondence analysis performed showed a clear-cut influence of some environmental variables on fish ecological categories distribution: the zone under continental freshwater discharges had higher pH and temperature measurements and housed more freshwater, estuarine resident, marine migrant and estuarine dependent freshwater species, while the site with marine influences had higher conductivity, salinity, transparency and dissolved oxygen data and was mainly associated with estuarine dependent marine species.