Multivariate morphometric investigation to delineate species diversity and stock structure of mud crab Scylla sp. along the coastal regions of Bangladesh

Abstract

Despite the importance of mud crab species (genus Scylla) in both coastal aquaculture and artisanal fisheries, knowledge of the species diversity and stock structure of mud crab population for their sustainable management across the coastal region of Bangladesh remains obscure. Therefore, the present study was conducted to delineate the diversity and stock structure of mud crab species based on the 24 morphometric length measurements and 27 morphometric ratios data collected from the three coastal regions (Chittagong, Cox's Bazar and Bagerhat) of Bangladesh. Based on the taxonomic keys, majority of the species (about 82.4%) were identified as S. olivacea, while the remaining (about 17.6%) was S. serrata. In consistent to our preliminary analysis, both the univariate proportion and multivariate analysis of the collected morphometric lengths and ratios data also distinctly divided the mud crabs population into two multivariate spaces as S. serrata and S. olivacea. For the further analysis of the stock structure of these two species, data were subjected to the univariate ANOVA, multivariate ANOVA, Canonical Variate Analysis (CVA), and Principal Component Analysis (PCA) according to their collection sites. Scatter plots of CVA scores between CV1 and CV2 and PCA scores between PC1 and PC2 showed that the individuals of both species clearly made clusters into three multivariate spaces with minimum overlaps according to their collection sites. In morphometric traits Linear Discriminant Function Analysis (LDFA), the average percentage of correctly classified (PCC) into the original groups of the S. olivacea and S. serrata was 100%. For stock discrimination, the average PCC into their original groups of collection sites were 100% and 99% for the S. olivacea and S. serrata, respectively. Finally, dendrogram based on the Euclidean distances consistently separated S. olivacea and S. serrata and stock structures similar to other multivariate analyses. In conclusion, our study shows that S. olivacea is the dominant mud crab species and S. serrata is the minor one, and the stock discrimination of each species should be considered in the management and conservation policy of these species along the coastal region of Bangladesh.