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

The effect of different combinations of tagging and release methods was exa mined on the survival, moulting, growth increment and recapture rates of sl ipper lobsters Thenus spp. on the Queensland (Australia) east coast using g eneralised linear modelling methods. Laboratory experiments indicated that while tagging is unlikely to significantly affect the survival rate or grow th increments of lobsters, it is likely to lower the incidence of moulting. In the field, recapture rates of tagged lobsters increased markedly by app lying 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 t o females. Reasons for this may be related to size differences between the sexes and how the fishers valued the rewards for different size classes. Th e 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 th an those with large tags. Two different methods of release were also compar ed; surface release and bottom cage release. Recapture rates of large lobst ers and those that were held on board for several hours prior to release we re 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 h ad significantly larger growth increments than males. (C) 2001 Elsevier Sci ence B.V. All rights reserved.