Monsoon cycle influences on catch and size of blue swimming crabs (Portunus pelagicus) from crab gillnets in Phetchaburi Province

Abstract

Portunus pelagicus is a crucial resource of Thailand and a large portion of the catch comes from artisanal fisheries. The aims of this study were to elucidate fishing practices and identify the effects of driving factors on catch in terms of quantity and quality of P. pelagicus caught by crab gillnets in Phetchaburi Province. Samples were collected from January 2018 to February 2019. In both upper and lower areas of Phetchaburi Province, the lowest catch per unit effort (CPUE) was found in the northeast monsoon season, while the highest was found in the pre-monsoon. The results indicated an interaction between areas, seasons, and mesh sizes on log CPUE, and the log CPUE was generally lower in the northeast monsoon season in both areas and groups of mesh sizes. The size of P. pelagicus by carapace width ranged from 5.5 to 17.0 cm with the median±interquartile of 11.0±1.0 cm. The crab size in the upper area was smaller than in the lower area in all seasons and the crab size in the southwest monsoon season was larger than in the other seasons for both areas. The median sizes were larger than the first maturity size of 9.5 cm in almost all the months, except October, in the upper area (median carapace width-interquartile = 9.0±0.8 cm).