Ichthyofaunal community assemblage and spatiotemporal patterns in the Bons Sinais Estuary, Mozambique: Ecological drivers and conservation implications

Understanding the ichthyofaunal assemblage of estuarine and adjacent coastal ecosystems is important for managing fishery resources and implementing conservation actions. This study explored the structure, diversity, and spatial-temporal variations of the ichthyofauna in the Bons Sinais Estuary (Mozambique) and the influence of environmental parameters. Fish sampling was conducted in the lower, middle, and upper zones using beach seine (active) and chicocota (fixed) gears in January 2020 and monthly from July 2020 to June 2021. The study identified 102 fish species, mostly of marine origin, belonging to 51 families. The most abundant families were Sciaenidae, Engraulidae, Clupeidae, Mugilidae, and Gobiidae, contributing over 78 % of the total catch. The most dominant species were Thryssa vitrirostris, Johnius dussumieri, Johnius dorsalis, Sardinella albella, Mugil cephalus, and Hilsa kelee, which accounted for more than half (52.43 %) of the abundance and 48.27 % of the biomass. The study found an ichthyofaunal community characterised by significant spatial variations, primarily influenced by salinity. The dominance of marine species in the lower and middle estuary contrasted with freshwater species in the upper zone. Dominant species showed spatial variations in abundance and biomass, but fewer showed seasonal variations. The middle estuary exhibited the highest species richness, diversity, and average abundance, while the lower zone had the highest biomass average. Threatened species, including Oreochromis mossambicus, comprised 3.4 % of the total abundance. These findings highlight the need for sustainable exploitation of fisheries resources and preserving the ecological functions of the Bons Sinais Estuary, which is important for resident and migratory species.