Stock assessment of the portunid crab, Charybdis natator (Herbst, 1794) (Brachyura, Portunidae) from the Gulf of Mannar coast, India

Fishery and stock assessment of the portunid crab Charybdis natator were studied for a one-year period along the Gulf of Mannar coast, India, mainly to assess these conditions along this stretch of coast. The primary aim of the study was to approach some precautionary measures that can be suggested for sustainable exploitation of the resource. For a rational exploitation of the crab resources in India, the present status of the stock should be known. The carapace width (CW) of C. natator ranged from 2.4 to 12.8 cm for males and 5.1 to 11.82 cm for females. The highest estimated total catch of C. natator was recorded from June to October. The male part of the population of this species was recorded more abundant than the female part along the Gulf of Mannar coast. The total stock, annual stock, annual catch, and exploitation rate for C. natator were, for males, 886.09 tonnes (t), 322.81 t, 51.65 t, and 0.058, and for females, 1923.92 t, 606.80 t, 30.34 t, and 0.016, respectively. The recruitment of C. natator was recorded throughout the year, with a peak in October and in May for males, and in September for females. The difference between the annual catch and Maximum Sustainable Yield (MSY) of C. natator was determined for males as 406.74 tonnes and for females 910.20 t. From this study, it could be concluded that a very low fishing pressure was imposed on C. natator, and that thus the resources of this species were underexploited at the Gulf of Mannar coast. Consequently, the present exploitation was less than the calculated MSY and the present effort could be increased for this underexploited resource along this stretch of coast. So it is suggested to increase the present level of effort by employing gill nets and crab pots along the coast of the Gulf of Mannar.