The fisheries and primary productivity of the Keta Lagoon
The Keta Lagoon in Ghana supports artisanal fisheries which comprise significant proportion of economic and dietary resources of the people. The state of the fisheries and primary productivity of the Keta Lagoon based on the two sites, Anloga and Woe, were studied from August, 2010 to March, 2011. A total of 22 finfish species belonging to 12 genera and 10 families were encountered in the Keta Lagoon. Fish species diversity based on Shannon-Wiener’s index (Hˈ), Species Richness based on Margalef’s index (D) and Species Evenness based on Pielou’s index (J) were generally low at both Anloga site at 1.27, 1.07 and 0.19, respectively and Woe site at 1.84, 1.75 and 0.25, respectively. The length-weight regression co-efficient (b) indicated that Tilapia zillii (3.12) and Tilapia guineensis (2.90) from Anloga sampling site as well as Sarotherodon melanotheron (2.66), Tilapia zillii (3.03), Tilapia guineensis (2.92) and Gerres melanopterus (3.13) from Woe sampling site grow isometrically. The condition factor (K) indicated that the fish species from Anloga site were in better condition than those from Woe. The Trophic Status Index based on Chlorophyll a estimation indicated that the lagoon was hypereutrophic. The high primary productivity was attributable to the high concentration levels of nutrients especially nitrate (95.31 mgl-1, 79.44 mgl-1) and phosphate (0.007 mgl-1, 0.005 mgl-1) form Anloga and Woe sites respectively contributed from farmlands situated around the lagoon through leaching. This was evident in decreased dissolved oxygen levels. Chloride levels were however at concentrations lethal to most of the fish species.