Distribution and population structure of deep-water crab Charybdis smithii (Decapoda : Portunidae) in the Arabian Sea and Bay of Bengal

The distribution and population characteristics of the potentially commercial deepwater crab Charybdis smithii were studied. The crabs were sampled during the research cruises of Fishery Oceanographic Research Vessel (FORV) SAGAR SAMPADA performed in the Arabian Sea and Bay of Bengal in 1985-1989. Samples were obtained from both pelagic and benthic zones. In the pleagic zone, the species was found almost throughout the study area with the maximum concentration in the offshore and inshore waters of the southwest coast of India. The highest densities of the benthic population were also found along the southwest coast of India (off Alleppey, 1740 kg h(-1)). In the benthic zone, the crab was recorded in the depth zone ranging between 60 and 356 m with a maximum average catch at 201-300 m in the Arabian Sea(23.1 kg h(-1)) and 150 m in the Bay of Bengal. A high percentage of pelagic hauls with C. smithii were from the oceanic province. In the Arabian Sea the pelagic crabs were found in almost all months, whereas benthic crabs were obtained only between July and January. The carapace width (CW) of crabs ranged from 11 to 72 mm CW and 11 to 69 mm CW for males and females, respectively. The crabs less than or equal to 31 mm CW were not found in the benthic catches. Juveniles less than or equal to 20 mm CW were only found in the pelagic zone with a high concentration in the oceanic province. Sex ratio of juvenile population was 1:1 but in most of the advanced size groups, a preponderance of males over females was noticed. Ovigerous females were found in the benthic zone and were totally absent in the pelagic samples.