Validation of Traditional Species Identification Techniques for Juvenile Mangrove Crabs (Scylla spp.)

Species identification of mangrove crabs at the juvenile stages is crucial for maximizing production. Traditional knowledge in identifying juvenile mangrove crabs (Scylla spp.) is mainstream although the techniques vary with locations and are yet to be validated for their effectiveness. In this study, widespread traditional techniques for identifying juvenile Scylla were validated by looking for patterns through principal component analysis in dorsal carapace features – including bumps, black spots, coloration, and shape – as determined by CL:ICW. The less prominent bumps on the dorsal carapace and the lower CL:ICW of S. olivacea were seen to have the potential for nationwide adoption to distinguish this least preferred species. The dorsal carapace color varies across species but is inconsistent across regions. The presence of black and white spots, texture features such as depression on the center of the dorsal carapace, and growth rates of the samples were found to have no diagnostic applications for juvenile Scylla. This study confirmed the utility of some traditional techniques to identify juvenile S. olivacea without the aid of a device, but no consistent method to differentiate S. serrata from S. tranquebarica was found. Image analysis data on these validated techniques can be added to the machine learning algorithm of existing species identification tools to increase accuracy.