The dynamics of the exploited population of Ethmalosa fimbriata (Bowdich, 1825, Clupeidae) in the Cross River Estuary and adjacent Gulf of Guinea

Abstract

Studies were conducted on the dynamics of the exploited population of Ethmalosa fimbriata (bonga) from purse seine fishery in the Cross River Estuary and adjacent Gulf of Guinea. Growth parameters were determined using the length–frequency distribution over an 18-month period. The asymptotic length, L ∞=35.95 cm total length, von Bertalanffy growth function, K=0.90, winter point, WP=0.1, signifies that growth slows down in February which was attributed to high temperature and reproductive activities. The longevity was 40 months. The instantaneous rate of total mortality, Z=6.91 per year, natural mortality, M=1.61 per year and fishing mortality, F=5.30 per year, were estimated. The current rate of exploitation ( E) was given as 0.77, indicating that the bonga stock is over-fished. From the yield-per-recruit analysis, E max, the exploitation rate giving maximum relative yield-per-recruit was estimated as 0.65, confirming that the stock is being over-fished. To reverse the overexploitation of the bonga stock in the Cross River Estuary, and the attendant adverse socio-economic consequences, it was suggested that effort should be reduced in the fishery and the economy of the fishing communities diversified.