Sierra Leone - State of the Marine Environment 2015

3. Marine Biodiversity

3.1. Plankton

3.3. Coastal fisheries

Several studies confirm the close correlation between the seasonal oscillations of hydrological conditions of the habitat, abundance variability of planktons, and fish abundance on the Sierra Leone shelf and the West African waters. The most recent study on plankton on the Sierra Leone shelf is found in Lamin (2011) and much emphasis is placed on the taxonomic diversity in relation to physic- chemical processes prevalent in 2008–10. The study recorded a taxonomic diversity of 49–61 zooplankton species from 20–24 genera/families, Calanoid copepods (30%) predominated throughout, followed by decapods. For over a period of about 50 years now the mean depth of the thermocline has not changed, and accordingly the bathymetric distribution of the major species assemblages has not changed either. Lamin (2011) further noted that surface temperature increased from 28.43 °C in May 2008 to 30.20 °C in May 2010, but this should be viewed as synoptic and inconclusive to be attributable to climate change. It could therefore be concluded that the plankton biodiversity has not shown any significant change over the past 2–3 decades, spatial distribution has remained fairly unchanged and oscillating with the seasons, whilst the relative predominance among plankton species in terms of biomass has changed with time as ecosystem trophic indices change. 3.2. Macro algae There are three major categories of algae with about thirty species in Sierra Leonean waters belonging to the following groups: Chlorophyta , Phaeophyta and Rhodophyta . In 2011, the seaweed Sargassum vulgare and recently (2014), Sargassum natans and Sargassum fluitans invaded the country’s coastal waters in unusually large amounts for the first time littering the entire coastline beaches. Since then this phenomenon seems to be a usual occurrence appearing around June and disappearing around October. During this period, activities such as fishing, navigation and tourism are being affected. The decaying plants produce an offensive odor on the beaches. This occurrence is now a national concern triggering studies initiated by the Environment Protection Agency Sierra Leone.

3.3.1. Fish species of the Sierra Leone coastal estuarine environment

The Sierra Leone River Estuary has been studied in Sierra Leone with respect to fisheries resources (Watts 1957, Longhurst 1965, Sentengo and Ansa-Emmin 1986), individual studies on single species or assemblages have also been undertaken by various workers including Pseudotolithus senegalensis and P. typus , Drepane africana (Beresford-Cole 1982), Pseudotolithus elongalensis , P. brachygnathus , P. typus , Pterocion peli , Pomadasys jubelini , Drepane africana , Chaetolipterus goreensis , Psettodes selchen , Galeoides decadatylus and Pentanemus quinquarus (Fofana 2000). As a matter of convention shrimps and crabs of estuaries and deltas are also included here. Only 3 ( Penaeus notialis, P. atlantica and P. kerathurus ) out of 6 species of shrimps are found in the coastal waters of Sierra Leone. There may be post larval stages and juveniles found in plankton. The species of crabs of commercial importance found in the Sierra Leone River estuary are the entire genus Callinectes and are Callinectes pallidus, C. amnicola and C. maginatus . 3.3.2. Ichthyofauna A large number of species of fish have been recorded for the Sierra Leone River estuary (as high as 80 species). The fishes of Sierra Leone estuary belong to two categories (Longhurst 1969, Fager and Longhurst 1968, Longhurst and Pauly 1987): Pelagic fish species and estuarine and creek species. 3.3.3. Pelagic fish community This is a rather diverse group and has been the subject of investigations for several years (Longhurst 1963, Williams 1968, Williams 1969, Villegas and Garcia 1983, Nieland 1980, Nieland 1982, Sentengo and Ansa-Emmin 1986, Anyangwa 1988, Coutin 1989). The dominant members of this group are the Clupeidae ( Ethmalosa fimbriata , Sardinella maderensis , Ilisha africana ). Others include: Carangidae (Caranx) and Chloroscombrus chrysurus . Some members of the Carangidae may make periodic incursions into the estuary at high tide: Decepterus rhonchus and Trachurus tracea . Tetraodontidae ( Lagocephalus cephalus , Liza falcipinis ), Sphyraenidae ( Sphyraena barracuda ), Pristis pristis , Dasyatidae ( Dasyatis margarita ). The inshore demersal stocks include mainly the Sciaenid fauna. Members of the Sciaenid assemblage live above the thermocline on shallow muddy bottoms. Although some

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