Studies on the exploitation and mortality of the crab Uca tangeri in Mbo river of Akwa Ibom State, Nigeria, was conducted for 12 consecutive months. Exploitation was calculated to be -1.62. The negative value could imply that the species is not fished or under-fished Length-frequency data was analyzed using FISAT software. Using the Shepherd’s method, asymptotic length (L∞) was 3.99cm, while the Von Bertalanffy Growth Function (VBGF) K was 0.10. Meanwhile, Powell-Wetheral plot estimated asymptotic length (L∞) was 3.58cm and Z/K was 0.72yr-1. The natural mortality(M) of Uca tangeri was 0.71yr-1. However, using length-converted catch curve, total mortality (Z) was estimated to be 0.27yr-1. The instantaneous fishing mortality (F) was calculated to be -0.44yr-1, indicating that it was not a highly fished species. Read more

The study of the relative yield and sex ratio of the West African fiddler crab (Uca tangeri) in Mbo river of Akwa Ibom State, Niger Delta, Nigeria, was conducted for 12 consecutive months. Uca tangeri exhibited sexual dimorphism with a sex ratio of 1.2:1.0, which was significantly biased in favour of males. The yield isopleths demonstrate the response of the crab to both variation in E (exploitation level) and Lc/L∞ (a proxy for mesh size). Yield contours with Lc/L∞ = 0.74 usually consist of four quadrants (Pauly and Soriano, 1986), each with its characteristics. The yield isopleths with Lc/L∞ = 0.74 and E = -1.62 belong to quadrant B, which implies that, large specimens were caught at high effort level. Read more