Movement, fishery sector impact, and factors affecting the recapture rate of tagged sand crabs, Portunus pelagicus (L.), in Moreton Bay, Queensland

Abstract

Selected mature male sand crabs (Portunus pelagicus) (6827 individuals with carapace widths of 120-192 mm) were tagged with Floy ED-68BA anchor tags and released in 14 areas of Moreton Bay and adjacent oceanic waters. In all, 1003 tagged crabs (14.7%) were recaptured, with 79% of these recaptured less than 2 km from their release points and 4% recaptured more than 10 km from their release points. Of the total recaptures, 63% were made within 14 days of crabs being released. Commercial pot fishers recaptured the largest proportion (70%) of crabs, whereas recreational fishers and commercial trawl fishers recaptured only 18 and 12% of tagged crabs, respectively. Recapture rates varied from 2 to 59%, depending on location, reflecting a massive spatial heterogeneity of fishing effort. Only 2.6% of recaptured crabs moulted between release and recapture. Crabs that were undamaged at release had twice the recapture rate of damaged crabs (i.e. crabs that had missing appendages), and the probability of recapture increased with crab size. Under laboratory conditions, unmodified Floy FD-68BA tags reduced the short-term survival of male P. pelagicus, possibly because of bacterial infection, and it was concluded that Floy anchor tags were not suitable for field growth studies of P. pelagicus.