Implications of the deteriorating environmental conditions of River Pra estuary (Ghana) for marine fish stocks

Abstract

Ghana’s marine fish stocks have been declining in the last two decades. Efforts to address this trend have focused mainly on curbing overcapacity, overexploitation and inappropriate fishing methods with little attention to degradation of the country’s coastal lagoons and estuaries, which serve as nursery habitats for juvenile marine fishes. To demonstrate the need to factor coastal ecosystems into fisheries management plans, this study assessed the quality of the waters of the River Pra Estuary, the second largest estuary in Ghana. This estuary is silted from activities of illegal alluvial gold miners upstream. Temperature, turbidity, salinity, conductivity, dissolved oxygen, pH, nitrate and phosphate concentrations were monitored from February 2012 to December 2013. Turbidities greater than 500 ppm known to have detrimental effects on estuarine organisms were recorded in the estuary from March to October each year. Dissolved oxygen concentration in the estuary in 2012 was below 5 mg/L, the threshold for survival of aquatic life in running waters. Although nitrate and phosphate concentrations in the estuary far exceeded the optimum levels (nitrate = 1.0 mg/L; phosphate = 0.1 mg/L) for primary productivity in estuaries, the high turbidity hampers light penetration and consequently limit primary productivity in the estuary. The possible effects of this estuary on recruitment of juvenile fish into the marine fishery are discussed with recommendations for management considerations.