The main objective of the study was to assess the abundance and distribution of sharks in Ghana’s coastal area. Samples were collected daily from the three sampling sites from April – to December 2021. The data obtained from this study were assessed for species abundance and composition, ecological indices; species diversity, and exploitation status using PAST and Microsoft Excel. A total of eight species were recorded with Prionace glauca (68%) as the dominant species and Carcharhinus leucas (1%) as the least dominant species. The mean species richness index (SRI) of 0.9 indicated infinite diversity of the species. The mean species evenness index (SEI) of 0.5 showed an evenly distributed species. The mean species dominance index (SDI) of 0.4 implied that the habitat was not dominated by only one or two particular species. The mean Shannon Weiner index (SWI) was less than 3, which is suggestive of pollution and habitat degradation. The exploitation status indicated that the stock of the shark species is in healthy condition. The month with the higher index was October which is possibly the aftermath of the close season and the major upwelling season. Extending the period of the closed season and reducing fishing effort are recommended.
This study aimed at assessing the growth and mortality parameters of the Prionace gluaca and Sphyrna lewini shark species from the coast of Ghana. Data was taken for nine (9) months from April 2021 to December 2021. The length data taken from the shark species was analyzed for the estimation of population parameters using the FiSAT II tool. From the results, the estimated asymptotic length (L∞) and the growth rate (K) of P. glauca and S. lewini were 396.4 cm and 0.27 yr–1 and 349.1 cm and 0.24 yr–1 respectively, indicating that these species exhibited slow growing characteristics, evinced by a longevity of approximately 11 – 12 years. The length at first capture (Lc50) for P. gluaca was 128.6 cm and that for S. lewini was 169.0 cm. The length at first maturity (Lm50) for P. gluaca and S. lewini was 179.74 cm and 160.4 cm respectively. By comparing the Lc50 and Lm50, it implies that individuals of P. gluaca were vulnerable to fishing gears before having the chance to mature and even spawn once. The total mortality (Z), natural mortality (M), fishing mortality (F) and the exploitation rates for P. glauca and S. lewini were 0.82 yr–1 , 0.22 yr–1 , 0.60 yr–1 and 0.73 and 0.76 yr–1, 0.21 yr–1, 0.55 yr–1 and 0.72, respectively. This suggests that fishing activities are the main cause of decline in the abundance of these shark species. The exploitation rate (E > 0.5) revealed that these species are overexploited in Ghana’s marine waters. Based on these findings, it is recommended that fishing effort be reduced through appropriate measures by relevant authorities. Vol. 9, No. 3, December 2022: 353-365
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