Wayne Sumpton

Localised movement of snapper (Pagrus auratus, Sparidae) in a large subtropical marine embayment

Snapper were tagged with dart and anchor tags in order to determine movement and the contribution of juveniles inhabiting estuarine areas to the offshore adult population. Laboratory experiments showed that loss of anchor tags was greater than dart tags, although this was not reflected in the results of field trials. A total of 6572 individuals were tagged in field experiments, of which 509 (7.7%) were recaptured. Only four of over 2500 fish tagged and released in Moreton Bay were recaptured in waters outside the bay, suggesting the bay is not an important source of recruits to the offshore fishery. However, problems associated with tag loss and mortality meant that the actual contribution of juveniles to the offshore fisheries remained unclear. Most snapper movements were localised; only ~1% of movements exceeded 100 km. Movements of snapper were mainly directed northward against the prevailing direction of the East Australian Current. Snapper were considered to be a suitable species for marine reserve protection owing to their relatively localised movement patterns.

Distribution of barnacle epizoites of the crab Portunus pelagicus in the Moreton Bay region, eastern Australia

The parasites of some decapod crustaceans are known to cause sterilisation of their hosts, and can thus have an important impact on the population dynamics of infested species. Blue swimmer crabs (Portunus pelagicus) collected in three areas around Moreton Bay, Australia were examined for the presence of epizoic barnacles in their branchial chambers and on their carapace. Of the 952 crabs inspected 92% were infested with Octolasmis spp. The mean number of barnacles (predominantly Octolasmis warwickii) per carapace and gill chamber (mainly O. angulata) were 2.35 and 71.1, respectively. Barnacle infestation of gills was found to differ significantly by area, season and sex with the deeper offshore areas exhibiting the highest number of barnacles. The distribution within the hosts showed barnacles were more likely to be distributed in areas closer to the inhalant aperture. Highest abundances were found on the proximal surface of the hypobranchial side of gills 3, 4 and 5. Host moult stage and parasitism by Sacculina granifera were also found to affect the abundance of epizoic barnacles in some areas.

Fine-scale spatial and seasonal partitioning among large sharks and other elasmobranchs in south-eastern Queensland, Australia

Our understanding of the ecological role of larger elasmobranchs is limited by a lack of information on their spatial and seasonal abundance. Analysis of 14 years of gill-net catch data in south-eastern Queensland, Australia, revealed that the species composition of large sharks and other elasmobranchs significantly differed among beaches and seasons. Spinner sharks (Carcharhinus brevipinna) and hammerhead sharks (Sphyrna spp.) comprised nearly half the catch of all elasmobranchs. Although the distribution of these sharks overlapped, spatial variation existed in their abundance. Spinner sharks characterised the catch at Sunshine Coast beaches, whereas the catch at Gold Coast beaches was dominated by hammerhead sharks. Seasonal differences in elasmobranch community structure were also apparent, driven largely by a lower abundance of many species during the winter and the predominance of species such as spinner sharks and hammerheads in spring and summer. The present study provides the first quantitative data for numerous species of Carcharhiniformes in south-eastern Queensland and demonstrates that analysis of catch-rate data can improve our understanding of how larger sharks partition resources.