Age and maturation of Loligo duvauceli and L. chinensis from Andaman Sea of Thailand

Estimated age, hatching date and sexual maturation were investigated for the loliginid squids Loligo duvauceli and L. chinensis, the commercially important neritic species in the Andaman Sea of Thailand. The specimens caught by commercial bottom-trawl in Phang-nga Bay and southern area off Phuket Island were obtained monthly from Phuket fish landing between April and August 2005. Age was estimated based on the counting of statolith increments from a total of 329 individuals of L. duvauceli (ML ranges from 41 to 224 mm) and 116 individuals of L. chinensis (ML ranges from 42 to 186 mm). The estimated age ranged from 41 to 161 and 67 to 158 days old for L. duvauceli and L. chinensis, respectively. The length–weight relationships differed among sexes and the sexual dimorphism was expressed as mature females having a greater body weight than males of the same length. Males showed a wide range of maturity size possibly because of the seasonal change in size at maturity. The results of the back calculation for the hatching date of individuals fell between November 2004 and June 2005 which suggests that L. duvauceli and L. chinensis hatch continuously and recruit to the fishing ground for a relatively short period with a shorter lifespan than expected.