Spatial dynamics of the South Australian rock lobster (Jasus edwardsii) fishery under a quota-based system

The southern rock lobster, Jasus edwardsii, is South Australia's most valuable fisheries resource, with an annual landed value Of C. AU$100 million. Approximately 80% of this revenue comes from the southern zone (SZ) rock lobster fishery, which has been managed under an individual transferable quota system since 1993. The total allowable commercial catch is currently set at 1900 tonnes. Long-term spatial trends in catch and effort were analysed over the period 1970-2005 to investigate possible changes in the spatial dynamics of the fleets as a result of quota introduction. Data indicate that the fishery contracted into three main Marine Fishing Areas (MFAs) after 1993. In particular, the long-term catch average in MFA 51 decreased from 185.4 tonnes pre-quota to 59.8 tonnes post quota. This MFA is located in the northern region of the SZ and is one of the furthest MFAs from the main fishing ports in the region. The fishery is also spatially contracted within MFAs. Approximately 80% of the annual catch comes from <60 m depth despite catch rates being 2-3 times greater in offshore sites as evidenced from both fishery-dependent and independent sources. Such trends appear driven by recent market preferences that select for small (<1 kg), red-coloured lobster that are primarily located on inshore grounds. As a result, fishers now target inshore sites to maximise returns under the quota-based system. The observed shift in the spatial dynamics of the SZ has clear implications for the biological performance indicators on which the fishery is managed. Specifically, the results highlight the need for a fishery-independent assessment of the resource that provides estimates of catch rate and biomass independent of current harvest strategies. Preliminary results from a trial survey undertaken in 2005/06 and 2006/07 show higher lobster abundance in lowly exploited offshore sites compared with inshore areas. These trends highlight the need for refined spatial management of the resource, which is the focus of the new management plan for the fishery.