Analyses of selected stock parameters of Dasyatis zugei (Müller & Henle, 1841) in Gulf of Mannar, Sri Lanka

Abstract

The pale edged stingray, Dasyatis zugei (Müller & Henle, 1841) is one of the major non-target species caught in the bottom-set crab nets used for catching Blue swimming crab (Portunus pelagicus) in Gulf of Mannar. Stock assessment of D. zugei will be needed to determine management measures to reduce its accidental catch. Hence, this study aimed at estimating the selected stock parameters of D. zugei in Gulf of Mannar. In total, 1,404 and 676 individuals were collected from 4.5-5.5-inch mesh-sized crab nets respectively in two landing sites Vankalai and Thalvupadu during September 2018 – July 2019. Disc width of all individuals was measured (mm), body weight was weighed (g) and sex was determined. Sex ratio of catch was 1:1.33 (male: female). Disc width ranged from 115 mm to 272 mm with the mean (±SD) and median of 174.86 ± 22.28 mm and 175.00 mm respectively. Disc width-weight relationship showed Log W = -1.906 + 0.1347 log WD for male and Log W = -2.774 + 2.286 log WD for female. The results show negative allometric growth (b<3) for both male and female of D. zugei. This concludes that D. zugei can grow faster in length than in weight. The stock status of D. zugei was determined using Length Based Spawning Potential Ratio model available in Barefoot ecologist toolbox and the result shows the Spawning Potential Ratio as 13%. The ratio ranges between 0% - 20%, it indicates that the population is overexploited. Results of the current study suggest that D. zugei population in the study area is over exploited. In conclusion, D. zugei population in Gulf of Mannar needs to be managed for a sustainable fishery.