Biological information and population features of mud crab, genus Scylla from mangrove areas of Sarawak, Malaysia

Abstract

This study was conducted to determine the size at maturity, size at mating, sex ratio and carapace width (CW) to body weight (BW) ratio of the most abundant mud crab species sampled in mangrove areas of Sarawak, Malaysia. Additionally, the taxonomic statuses of Scylla spp. mud crabs from this area were assessed. A total of 14,000 mud crabs representing different sizes, sexes and species were examined to determine taxonomic status and sex ratio for each. In addition, 2000 mud crabs were randomly measured to determine the CW–BW relationship. A total of 1724 female crabs and 1230 male crabs of various sizes were randomly sampled to determine the size at maturity and size at mating. The results indicate that the size at maturity of female S. olivacea and S. tranquebarica were 8.6 cm CW and 9.2 cm CW, respectively. The size at maturity of male crabs is very similar but could not be confirmed because all S. olivacea and S. tranquebarica individuals sampled were already mature. Size at mating for female and male S. olivacea was 9.6 cm CW and 11.3 cm CW, respectively. For female and male S. tranquebarica, size at mating was 10.8 cm CW and 13.1 cm CW, respectively. S. olivacea was the most common mud crab species in this area, comprising 77.64% of total species, followed by S. tranquebarica (21.91%) and S. paramamosain (0.45%). S. serrata were not found during this study. The sex ratios (male:female) for S. olivacea and S. tranquebarica were 1:0.89 and 1:0.75, respectively. The BW increment rate for male crabs of S. olivacea and S. tranquebarica were higher relative to that for female crabs. The CW–BW relationship shows that S. tranquebarica was heavier than S. olivacea. The study also indicates that the selective fishing of mature crabs at a particular site where S. olivacea and S. tranquebarica occur together can cause negative impacts on the populations of these species by affecting size at maturity, size at mating and population dynamics. The biological information and population features from this study can be used in sustainable management and exploitation of mud crab resources in Malaysian coastal waters and the South China Sea.