POPULATION STRUCTURE OF THE THREE-SPOT SWIMMING CRAB Portunus sanguinolentus (HERBST, 1783) (CRUSTACEA: BRACHYURA: PORTUNIDAE) OF THE GULF OF MANNAR, SOUTH EAST COAST, INDIA

The crab fishery in India is fast developing, and there is vast scope for crab meat, both at national and international markets. The three spotted swimming crab, P. sanguinolentus, is one of the most common and commercially important crab found along the east cost of India. Among the maritime states, Tamil Nadu ranks first in crab landings. More number of crabs was landed at Gulf of Mannar and Palk Bay. The main aim of this study was to know the stock level of P.sanguinolentus and its current intensity of exploitation in Gulf of Mannar. The stock assessment of the portunid crab P. sanguinolentus was studied for one year along the Gulf of Mannar coast. The sampling stations were Therespuram, Vellapatti, Vedalai and Periyapattinam. Fortnightly samples were collected from these landing centers and each crab was measured and recorded for its sex, carapace width, carapace length, abdomen width, chelate length and body weight by using Vernier caliper. The catch and effort data and landings of crabs were recorded on the sampling day. The data were analyzed by using FiSAT II software.

P. sanguinolentus was available throughout the year at Gulf of Mannar coast. In general, this species were abundant in shallow depth of 10 - 15 m. The bottom set gill net is mainly used for crab fishing and it is locally called as 'nandu vallai'.

The recruits of P. sanguinolentus were recorded throughout the year with peak during September for males and November for females. The fishing mortality of adult males and females of P.sanguinolentus were found to be high.  

The natural mortality was high in the length group of size less than 7cm. The difference between the annual catch and MSY for males was 0.34 t and for females was 0.82 t. The present exploitation for male and female was almost equal to the MSY.

Hence, the present effort could be continued without any increase to obtain biologically optimum yield. Crabs have high consumer demand and the resource needs proper management for its sustenance.