Temporal and spatial patterns of demersal fish assemblages in the coastal water of Sierra Leone

Information on the temporal and spatial patterns of fish community is key to further understand the functioning of marine ecosystem and protect marine organism resources efficiently. 6 demersal trawl surveys were carried out in the coast water of Sierra Leone during Sep 2019∼May 2021. Obvious temporal and spatial heterogeneity of oceanographic condition were observed in the survey area, the water temperature and salinity were usually higher in dry season and lower in rainy season. A total of 195 species belong to 79 families were identified. Offshore Sciaenid sub-community and Inshore sparid sub-community were the 2 common and major groups identified from 6 surveys, but the composition of dominant species may have changed. Less abundant of some traditional economic species (P. Typ, P. qui, Epinephelus, Arius and Lutjanus) and more abundant of T. myo were caught The Offshore sciaenid sub-community distributed mainly in southeast part or closed to shoreline in north part of survey area. The Inshore sparid sub-community distributed mainly in northwest part. Bottom sediment type (Btype) and depth were the common significant factors for the special pattern of fish community in all surveys. Offshore sciaenid sub-community was always associated with mud substrate and shallow water; Inshore sparid sub-community was associated with sand substrate and most of sites distributed in deeper water. The significant effect of sea surface salinity (SSS) were only observed in Oct, Dec, Jan and May. SSS was filtered as significant environment parameter, may not just base on the effect of salinity on fish community, but SSS was also a better characteristic parameter for monthly fluctuation of oceanographic condition. The increasing fishing activities maybe the one of major disturbance factors to the structure change of fish community. In order to promote the biodiversity conservation, strengthen fishery management based on ecosystem approach and developing sustainable fishery should be advocated. •The obvious temporal and spatial heterogeneity of oceanographic condition were observed in the coast water of Sierra Leone. The water temperature and salinity were usually Higher in dry season and lower in rainy season. The fluctuation of oceanographic condition lag behind season variation of climate.•2 common groups (Offshore sciaenid sub-community and Inshore sparid sub-community) were identified in 6 survey of this study. Less abundant of some traditional economic species (P. Typ,