Growth, mortality and size structure of the Ridged swimming crab Charybdis natator Herbst, 1789 was assessed based on samples collected from the Gulf of Mannar, southeast coast of India, between June 2015 to June 2016. The carapace width of the species ranged from 2.4 to 12.8 cm for males and 5.1to 11.82 cm for females, the carapace length ranged from 2.3 to 9.5 cm for males and for females from 1.9to 8.6 cm. Weight ranged from 20 to 659 g for males and 28 to 268 g for females. The estimated asymptotic length (L∞) and growth co-efficient (K) for males and females were 14.18 cm and 13.20 cm and 1.20 y-1 and 1.52 y-1 respectively. The mortality parameters Z, M, F and E for males (Z=2.52; M = 2.51; F= 0.16; E= 0.063) and females (Z= 3.00; M = 2.99; F= 0.05; E = 0.016) were estimated. The factor explaining the relationship between natural mortality coefficient and physical factor M/K was 2.09 and 1.96 for males and females of C. natator. As the fishing mortality is less compared to the natural mortality, the results
indicate that the population of C. natator in the Gulf of Mannar is underexploited.

Size structure, growth parameters, mortality parameters, Charybdis natator, Gulf of Mannar