The Philippine Journal of Fisheries 28(1): 17-32 January - June 2021 DOI: 10.31398/tpjf/28.1.2020A0002 RESEARCH ARTICLE Assessment of Mud Crab Fishery in Panguil Bay Celestina Q. Jumawan1, Ephrime B. Metillo2 * , Juvenry P. Polistico1 1National Fisheries Research and Development Institute−Brackishwater Fisheries Research and Development Center−Lala, Lanao del Norte 2Department of Marine Science, Mindanao State University-Iligan Institute of Technology, Bonifacio Ave., Tibanga, Iligan City ABSTRACT The last assessment of three commercially important mud crab species Scylla( tranquebarica, S. olivacea and S. serrata) in the mangrove dominated Panguil Bay was in 2005; there was already an indication of the stock decline. This study aimed to continue the assessment but focused on production, growth parameters, total mortality, and exploitation rate of the three mud crab species at seven mud crab landing sites from March 2017 to March 2019 following standard fisheries enumeration protocols. Results showed that the total resource production in Panguil Bay decreased from 201.1 MT in 2005 to 103.0 MT in 2017-2019. Growth parameters of the three species for male and female, respectively are as follows: S. tranquebarica (L∞ = 11.5 cm and 11.7 cm, annual growth coefficient K = 0.6 and 0.6, exploitation rate E of 0.5 and 0.5); S. olivacea (L∞ =10.9 cm and 11.4 cm, K = 0.5 and 0.6, E = 0.6 and 0.5); and S. serrata (L∞ = 12.3 cm and 12.9 cm, K = 0.7 and 0.6, E = 0.6 and 0.6). Total production of mud crabs increased, and the three species are highly exploited, but exploitation rates are already slightly below or above maximum sustainable yield (Emax). A total of 1,848 fishers were recorded owning 2,015 boats composed of 1,419 motorized and 596 non-motorized. An inventory showed an increase of 5.36% in the number of motorized boats from the last assessment in 2005. A total of 15 types of gear were recorded, in which the top three include fish corral, crab pot, and gill net. Consequently, this study recommends reducing the present fishing pressure or effort of the three mud crab species, particularly during the spawning season occurring on wet months (July to October), for sustained mud crab fisheries in Panguil Bay. *Corresponding Author: [email protected] Keywords: Stock assessment, mudcrab, Received: August 13, 2020 exploitation rate, Panguil Bay Accepted: December 23, 2020 1. INTRODUCTION Mud crabs are known to be at the top of the list of export-earning aquatic resources in Panguil anguil Bay is a small but rich fishing ground Bay due to their high demand and reasonable price that supports thousands of small-scale fishers (Rivera et al. 2017). The export of mud crab from in northwestern Mindanao. Historically it is Panguil Bay has widely increased over time due to its Pa rich fishing ground of wild shrimps and crabs. In huge availability and high demand in the live mud the past study conducted by Jimenez et al. (2009), it crab market (Rivera et al. 2017). This market scenario was observed that the landed catch of crustaceans may result in high mud crab fishing activities and was dominated by three mud crab species, namely: eventually a sudden decrease of the stock. However, the giant mud crab (Scylla serrata), purple mud crab existing knowledge about the status of the stock of (S. tranquebarica), and orange mud crab the three mud crab species in Panguil Bay is unclear (S. olivacea). Since 2005, very few follow-up studies since its previous stock assessment study (Jimenez et have been carried out on the fisheries biology of al. 2009). these commercially important crab species (Jimenez Regulatory instruments such as spatial and et al. 2009). The three species and the fourth temporal restrictions, gear ban, and mesh regulations S. paramamosain are now resolved as four distinct need to be undertaken. They must still be based on Scylla species (Fazhan et al. 2020). scientific data to attain sustainable fisheries and 17 | The Philippine Journal of Fisheries Jumawan et al. / The Philippine Journal of Fisheries 28(1): 17-32 rational resource management (Dickson 2009). with the mud crab fishery; Policy measures need to be supported with data 4. Determine the Catch Per Unit Effort (CPUE); and from assessments that yield biological information 5. Determine the sex ratio, gonad maturity, and GSI of (Jimenez et al. 2009). Stock assessment is one way the three mud crab species. to check a particular fishery's status before a policy recommendation is lobbied. Before a policy could 2. MATERIALS AND METHODS take effect, comprehensive scientific data will have to be produced as the basis. Hence, this study aims to 2.1 Landing centers/sampling areas conduct a stock assessment of the mud crab fishery in Panguil Bay. Specifically, it seeks to: The sampling stations were established based on the known coastal landing areas in Panguil 1. Assess the population parameters and Bay identified in 2005 (Jimenez et al. 2009), namely: recruitment patterns of the three mud crab species Municipalities of Kapatagan, Lala, Baroy and (S. tranquebarica, S. olivacea, S. serrata) in Panguil Kolambugan in Lanao del Norte; Tangub City and Bay; the Municipality of Bonifacio, Misamis Occidental; 2. Make an inventory of fisherfolk fishing boat and and the Municipality of Aurora, Zamboanga del Sur gears involved with mud crab fishery; (Figure 1). The sampling at these sites would allow 3. Know the catch species composition associated comparison of results between this and past studies. Figure 1. Map showing the location of mud crab landing sites at Panguil Bay where sampling for this study was undertaken. Insert is the map of the Republic of the Philippines showing the location of Panguil Bay (square). 18 | The Philippine Journal of Fisheries Assessment of Mud Crab Fishery in Panguil Bay 2.2 Data collection annual habitat temperature of 30°C. Z is the total instantaneous mortality, M is natural mortality, and F Data on the number of fisherfolk, fishing is mortality caused by fishing. The instantaneous Total boat, and gear were collected and recorded by the Mortality (Z) was estimated following the formula: enumerators from the fisherfolk registry of the Office of the Municipal Agriculturist (MAO). On-site Z = M + F fisheries enumeration was done to validate the records. Landed catch survey of the three mud Expanding the equation for mortality would crab species, namely, S. serrata, S. olivacea and S. lead to the estimation of Exploitation Rate (E) via the tranquebarica was conducted from March 2017 to following equation: May 2019 by trained fisherfolk enumerators using a standard survey form on catch and effort. The E = F survey was done for two days intervals or 20 days in Z a month, including Saturdays, Sundays, and holidays. Sex of mud crabs was determined, and the survey Level of exploitation of stocks used the forms (see Appendix A) include the following data following categories: (a) E below -10% of E0.1 suggests gathered: biological parameters carapace length (CL) underexploited; (b) E = -10% of E0.1 to E = +10% of E0.1, to the nearest 0.1 cm using the vernier caliper and optimally exploited; (c) E above +10% of E0.1 to below body weight (BW) to the nearest 0.1 g using digital E = E0.1, overexploited; and (d) E equal to or above E0.5, weighing, landing site, fishing ground, the volume of highly overexploited. E values were also compared catch per species, type and number of gear and boat with predicted Emax (exploitation rate, which produces used, and the number of fishing operation hours. All maximum yield) to discern if the stock’s exploitation survey forms were collated and processed monthly. level is beyond the maximum sustainable yield level. Beverton and Holt’s relative yield per 2.3 Data analysis recruitment (Y/R) and relative biomass-per recruitment (B/R) as a function of E (exploitation rate), 2.3.1 Population parameters E0.1 (exploitation rate value where slope or marginal increase in Y/R with increasing E is 1/10 of that at E The mud crab length-frequency data from = very near-zero levels), E0.5 (value of E under which the major fishing gears, namely fish corral, crab pot, the stock has been reduced to 50% of its unexploited and gill net, were analyzed. Carapace length of mud biomass), and Emax of each species was estimated using crab samples per month was measured to construct the Beverton and Holt Analysis facility through knife- the length-frequency data. The data were processed edge selection procedure in FISAT II. using the FAO-ICLARM Stock Assessment Tool or FiSAT II version 1.2.2 software (Gayanilo et al. 1997). 2.3.2 Catch and species composition Annual recruitment patterns were derived for males and females of the three mud crab species also using Apart from recording the three mud crab FiSAT II. Growth parameters were determined first species, the composition of the other species caught by estimating the initial asymptotic length (L∞) and by fish corral, crab pot, and gill net in the bay was the ratio of the total mortality to growth coefficient listed and identified up to species level. The fishery (Z/K) using the Power-Wetherall method (Gayanilo resources were categorized into fish, invertebrates, and Pauly 1997) based on the equation of Beverton and other organisms. The total catch value of each and Holt method (1956). The initial seed value of species by gear for the year was computed and ranked L∞ was further analyzed in ELEFAN I (Electronic from highest to lowest.