Documentation and validation of selected traditional practices of Philippine fishermen in species identification of juvenile mangrove crabs (Scylla spp.)

• Main Author: Orario, Hilarie P.
• Format: text
• Language: English
• Published: Animo Repository 2022
• Subjects: Scylla (Crustacea); Biology
• Online Access: https://animorepository.dlsu.edu.ph/etdm_bio/21; https://animorepository.dlsu.edu.ph/cgi/viewcontent.cgi?article=1022&context=etdm_bio
• Institution: De La Salle University

Mangrove crabs (Scylla spp.) are high value commodities in the Philippines and the Asia-Pacific. Three of the four Scylla species have been recorded in wild populations in the Philippines: S. serrata, S. olivacea, and S. tranquebarica. Majority of juvenile mangrove crabs for grow-out are still sourced from wild populations. Growers have differing species preferences depending on their goal, but wild populations are made up of the three species due to their overlapping ranges. To better secure production gain, fishermen need to distinguish the species they prefer before crab farming. Traditional techniques to identify mangrove crablets exist but they vary across locations and have yet to be validated for their effectiveness. This study documented the traditional techniques used by Philippine fishermen to identify juvenile Scylla species. Widespread traditional techniques that can be feasibly evaluated were validated. Principal component analysis of the morphological variations of the samples pre- and post-experiment revealed that the species samples exhibit a pattern for bumps on the dorsal carapace; black spots on the dorsal carapace; coloration of the dorsal carapace; and the shape of the carapace as determined by the ratio of carapace length to internal carapace width (CL:ICW). Further analyses were done to determine the potential scale of utility of these features. The characteristic bumps on the dorsal carapace which are more prominent in S. tranquebarica and S. serrata compared to S. olivacea; and the lower CL:ICW of S. olivacea translating to its wider shell compared to that of S. serrata’s and S. tranquebarica’s were found to have the potential for nationwide adoption. The dorsal carapace color is found to have a potential for use in Cagayan, Camarines Norte, and Sorsogon. Color patterns such as black spots and white spots; texture features such as depression on the center of the dorsal carapace; and growth rates of the samples using CL and ICW were found to have no diagnostic function for juvenile Scylla. This study confirmed the utility of traditional techniques to identify juvenile Scylla without the aid of a device. Quantitative measurement of the features of validated techniques may also be done to establish patterns for developing a technology that relies on these traditional techniques as basis for species identification.