Title: Fish species abundance and distribution in The Gambia estuary

Final project
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The area covered by this study extends from the mouth of the Gambia estuary to about 250 km inland. In this stretch of the estuary, about 43 seining sampling stations were operated. The purpose of this study is to look closely at the fish resources of the estuary with the view of improving understanding of existing patterns that determine periodic yields as a prerequisite for rational and sustainable management, which has to be based on sound scientific findings. Understanding the fish resource patterns and trends of factors that affect it would facilitate review and enable proper formulation of legislation governing its sustainable exploitation. The results are expected to help explain past, present and future yield patterns as well as provide a basis for planning and implementation of future estuarine-related projects. In the report, environmental parameters such as water temperature, salinity, dissolved oxygen, water transparency and depth are observed as well as fish species occurrence within the estuary. In sum, during the five surveys conducted throughout the estuary, surface water temperatures did not differ much from bottom temperatures. The small difference between mean surface temperature and bottom temperature (0.68°C) indicates an absence of a thermocline in the Gambia estuary even during the rainy season. Records of salinity throughout the surveys indicate a negative upstream gradient with slopes differing from survey to survey depending on the volume of down stream flow of freshwater. The results of the study indicate surface and bottom concentration of dissolved oxygen in a parallel pattern of oscillation throughout the estuary with a mean difference of only about 0.29 mg/l. On the whole, the lower estuarine waters were observed to be relatively more turbid from September to May, while the upper estuarine turbidity was observed to be highest in April to September. Turbidity appears closely linked to river discharge regime. About 80 fish and shellfish species were encountered in the Gambia estuarine system belonging to more than 40 families. Salinity seems to be the main factor controlling the occurrence of species throughout the Gambia estuary.

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