Reproductive status of the blood-spotted swimming crab, Portunus sanguinolentus (Herbst, 1783) (Brachyura, Portunidae) landed off Cochin, India

Abstract

Abstract Portunus sanguinolentus (Herbst, 1783) is an important commercial crab with a wide distribution along the Indian coast. In Kerala it is landed mainly in trawls, and ranks first in the landings in most years, recording about 50% of the crab landings of the state during 2012-2019, with the exception of 2014. Females dominate the fishery and their sizes range between 55 and 170 mm carapace width (CW), with 90-110 mm being dominant in the landings. Berried females are recorded throughout the year, without any regular dominance in a particular month, although during March-May good percentages of these are observed in overall landings. Newly spawned eggs are bright yellow/orange in colour, with an average size of 270 μm, and by the time of hatching the colour changes to dark grey, and it takes 8-10 days to hatch to the first zoea stage. Fecundity in numbers of eggs varied between 80 960 and 2 357 004 with an average of 512 914 for females of different size groups from 81 to 170 mm CW. Captive studies showed that the species is capable of multiple spawnings, with a maximum of three in an intermoult cycle. Size at maturity (LM50) in females was estimated at 86.5 mm CW and in males at 80.1 mm CW. All the females were mature above 120 mm CW and mature females below 70 mm CW were not recorded in the landed crabs. The smallest size of the mature and berried females recorded in the landings was 71 mm CW/22 g and 80 mm CW/32 g, respectively. In the landings, males comprised sizes between 51-170 mm carapace width (CW) with 91-105 mm forming the major size group contributing to the fishery. In males, 100% maturity was observed in crabs above the size of 95 mm CW, whereas sizes below 60 mm CW were immature. The smallest size of the mature male crab recorded in the landings was 60 mm CW/16 g. Minimum Legal Size (MLS) was implemented in the state in 2016 and for P. sanguinolentus. MLS is fixed at 70 mm CW and it has been proven that this helps in the sustainable utilization of the resource.