Movement within and between different habitats by the portunid crab Scylla serrata

Abstract

Tagging experiments were carried out on Scylla serrata in three different types of habitat in Moreton Bay, Queensland, Australia, during 1976–1981. A total of 6 233 crabs were tagged and 1 180 recaptured. Two categories of movement were found, a free ranging type and an offshore migration by females. Crabs in a narrow creek with mangrove-covered banks displayed little movement. In areas with large intertidal flats bare of mangroves, crabs underwent more movement and adults (carapace width 150 mm or greater) and subadults (carapace width 100 to 149 mm) moved similar distances (mean 3.9 km). In an area with direct access to the sea, males and females moved equal distances, but in a long channel behind an island, mean female movement (6.6 km) was significantly more than that of males (mean 3.7 km). The distance between tag and recapture site was not greatly affected by the time at liberty over a period of 1 to 36 wk. Tag recaptures showed an exchange between the populations of a mangrove creek and those in the neighbouring bay. There was very limited exchange between the population in an estuary and the adjacent bay and no exchange was found between neighbouring areas separated by a region of habitat unsuitable for S. serrata. None of the more than 3 000 females captured in the study area was carrying eggs, but two tagged ovigerous females were caught at sea after having moved out of the study area. Eight other females were recaptured in other inshore or estuarine areas 20 to 65 km from their release site.