Assessment of the fishery of a stunted population of the cichlid, Sarotherodon melanotheron (Rüppel), in a "closed" lagoon in Ghana

This aper examines the status of the tilapia fishery in Fosu Lagoon at Cape Coast, inthe Central Region of GLana (5°07’ N,1°6’ W). The blackchin tilaia, Sarotherodon melanotheron (Rüppel), constitutes about 90 % by weight of the total fish catch, and the annual yield of 452—664 kg/ha is apreciably higher than those reported for other tropical lagoons. Variations in the CPUE (0·30—0·96 kg/man-h) were related to fluctuations in the water level of the lagoon. Using the ELEFAN method, estimates of the growth and mortality parameters, based on length-frequency data were: Loo = 16·1 cm TL, K = 0·82/ yr, Z = 4·95/yr, M = 1·90/yr and F = 3·05/yr. The growth estimates and the maturity-length ratio suggest that the population is stunted. The mean length at first capture(Lcso) was estimated to be 6·2 cm TL. Although the present rate of exploitation (E= 0·62) appears high, an analysis of the relative yield-er-recruit (Y/R) and highrecruitment shows that this exploitation rate can be maintained by the Egoon population. Recruitment occurs throughout the year with two peaks, and this probably ensures the sustenance of the high yield.