Estimated growth of the mud crab Scylla olivacea in the Ranong mangrove ecosystem, Thailand, based on a tagging and recapture study

Abstract

Growth of the mud crab Scylla olivacea in the Ranong mangrove ecosystem was estimated using a size-transition matrix. Male (n = 1284) and female (n = 1069) mud crabs were tagged with externally visible and numbered T-tags and then released. Tagged crabs caught by commercial small-scale fishermen were measured and re-released. Data from 664 male and 463 female recaptures were obtained in total. Moult increment in the investigated size range (5–13 cm external carapace width) was independent of size and sex. The size distribution of mud crab moult increments was fitted to a normal distribution, resulting in a mean moult increment of 1.67 ± 0.48 cm (s.d.). This result was used to estimate the proportion of males and females moulting, and the selectivity of the baited traps used to catch them. Trap selectivity among the tagged crabs was uniform for both male and female crabs. Also, the proportion of those moulting decreased with size in the same manner for both sexes. The predictions of growth from the final size-transition matrix were in agreement with the observed growth of a subset of tagged crabs not used in the estimation of parameters in the size-transition matrix and growth of crabs reared in captivity over a period of 2 months.