The food of the demersal fish of a West African estuary.

As part of a project to investigate the relationship between the West African demersal fish and the marine benthic communities, an analysis of the food and feeding intensity of the fish commonly taken in otter-trawls in the Sierra Leone River was undertaken by this Institute in 1952. A quantitative survey of the benthos, and a study of its community structure, is now nearing completion in the same area. The study of the food of demersal fish was confined by practical considerations to the Sierra Leone River, which is convenient to these laboratories and calm enough to be worked at all seasons by the open launches used in the period 1952-55. The term 'Sierra Leone River' is applied to the large and open estuary of the Rokel River; at the mouth, between Cape Sierra Leone and the Bullom Shore, it is almost ten miles wide. Into this estuary flow the effluents of the Rokel River, of several smaller rivers, and of innumerable serpentine creeks draining mangrove flats. There is no bar across the mouth, and the main channel is 10-12 fm deep, so that there is free influx of marine organisms. From May to October, during the rainy season, conditions of lowered salinity extend right to the mouth, while during the dry season there is a considerable inflowing of sea water. The tidal streams are strong, reaching 5 kn on the ebb of springs, and much transport of deposits occurs, so that the nature of the bottom at any one place may change radically over a period of only a few months. Demersal fish, of which the majority are euryhaline, are present in the estuary throughout the year and are much fished from canoes with hand and long-lines.