Seasonal abundance and recruitment in an estuarine population of mud crabs, Scylla paramamosain, in the Mekong Delta, Vietnam

Abstract

Artisanal fisheries for mud crabs are an important source of income in coastal communities of the Mekong Delta. However, populations are subject to pressure from increasing fishing effort to provide seed crabs for pond culture, as well as diminishing mangrove habitats. In the present study, Scylla paramamosain was found to be the dominant mud crab species within an estuarine mangal system, representing over 96.8% of mud crab fishery landings between February 1998 and March 1999. S. olivacea was also present in relatively low abundance (3.2% of landings). Analysis of catch-per-unit-effort (CPUE) data collected throughout 1997 and 1998, for an intertidal hand-fishery, shows that mud crabs were present in a fairly narrow range of mean abundance throughout the year, despite protracted periods of freshwater conditions during the rainy season. Recruitment of juvenile S. paramamosain (3–4 cm carapace width) was continuous through 1998, with a significant peak at the beginning of the dry season. No juvenile S. olivacea (< 5 cm carapace width) were found during the study. The mangal appears to provide a nursery habitat for S. paramamosain, with predominantly juveniles and sub-adults present, while a higher proportion of adults were recorded in the sub-tidal component of the population. Mature females were present throughout the year, with a peak in September–October 1997. The CPUE analysis provides a baseline of seasonal variation in crab abundance that can be used to monitor the effectiveness of resource management and potential impacts of future changes in habitat.