Population dynamics of Scyllarid lobsters of the genus Thenus spp. on the Queensland (Australia) east coast. I. Assessing the effects of tagging

Abstract

The effect of different combinations of tagging and release methods was examined on the survival, moulting, growth increment and recapture rates of slipper lobsters Thenus spp. on the Queensland (Australia) east coast using generalised linear modelling methods. Laboratory experiments indicated that while tagging is unlikely to significantly affect the survival rate or growth increments of lobsters, it is likely to lower the incidence of moulting. In the field, recapture rates of tagged lobsters increased markedly by applying an antibiotic/antifungal ointment to the tag wound and by minimising the length of time lobsters were held on board prior to release. Recapture rates for Thenus orientalis declined by about 0.5% for every hour lobsters were held on board prior to release, even though they were kept in aerated seawater. About twice as many male T. orientalis were recaptured compared to females. Reasons for this may be related to size differences between the sexes and how the fishers valued the rewards for different size classes. The size of the T-bar anchor tag affected recapture rates of Thenus indicus; recapture rates of lobsters tagged with small tags were about 33% higher than those with large tags. Two different methods of release were also compared; surface release and bottom cage release. Recapture rates of large lobsters and those that were held on board for several hours prior to release were improved by using the bottom cage method. However, under some conditions, the cage may lower recapture rates relative to the surface release method, possibly because of increased stress and trauma from crowding in the cage. For both species, growth increments of recaptured lobsters increased with the period at liberty and declined with increasing lobster size. Females had significantly larger growth increments than males.