Management implications of sex ratios of three palaemonid shrimp in the Cross River Estuary, south eastern Nigeria

Information on sex composition of fish/shellfish species is important in determining reproductive potentials and estimating size structure of a given stock. Sustainable fisheries management options and policies usually rely on this aspect of the reproductive biology. In the present study, the sex ratios of three palaemonid shrimps, Macrobrachium macrobrachion, Macrobrachium vollenhovenii and Macrobrachium equidens were studied over an annual cycle with respect to gear type. Male: female relationship for M. macrobrachion caught with beach seine, pushnet and trap were 1:2.2, 1:2.1 and 1:2.15 respectively, while the M:F ratios for M. vollenhovenii were 1:1.27 (beach seine), 1:1.32 (pushnet) and 1:1.64 (trap). The overall M:F ratios during the annual cycle were 1:2.15 (M. macrobrachion), 1:1.47 (M. vollenhovenii), and 1:1.74 (M. equidens). The monthly sex ratios indicated that there were more females than males during the period, except for M. equidens which had a ratio of 1:0.78 in the month of August. This is advantageous for the stock dynamics of the species, especially if the males could mate with more than one female during any reproductive season.