Southern zone rock lobster (Jasus edwardsii) fishery stock assessment 2019/20: report to PIRSA Fisheries and Aquaculture

ABSTRACT

This stock assessment determined the status of South Australia's Southern Zone Rock Lobster Fishery (SZRLF) and provides the latest estimates of the biological performance indicators (Pis) information in context of the reference points (RPs) and stock status classification described in the Management Plan for the fishery (PIRSA 2020). Stock status was determined using the harvest strategy for the fishery that was developed in alignment with the National Fishery Status Reporting Framework (NFSRF) classification system that is used to determine the status of all South Australian fish stocks. Assessment of the SZRLF relies heavily on data from the commercial fishing sector through mandatory catch and effort logbook reporting. Catch per unit effort (CPUE) of legal and undersized (pre-recruit) lobsters are the main indicators of legal and pre-recruit abundance. Fishery-independent surveys and fishery model outputs also contribute to the assessment. During the 2019 fishing season (i.e. 1 October 2019 to 31 May 2020), the fishery was impacted by the COVID-19 market closure in late January of 2020. The primary impact was a considerable reduction in catch in February (6 t in 2020), where normally up to 100 t is landed. Consequently, the 2019 TACC (1,246 t) was not fully taken with a total commercial logbook catch of 1,202.4 t (96% of TACC). Effort required to take the catch was 758,029 potlifts, the lowest on record. Nominal legal-sized CPUE in 2019 was 1.59 kg/potlift, reflecting a 65% increase over the last three seasons and the highest catch rate since 2005. Current legal-sized catch rates are now above both the long-term average and the trigger reference point (TrRP) for the fishery. Recent increases in CPUE are also reflected in fishery-independent surveys. The pre-recruit index (PRI) shows a long-term decline since the late 1990s with the 2015 estimate the lowest on record Over the last four seasons, the PRI has increased by 138% to 1.76 undersized/pot, the highest since 2002. In the SZRLF, the time taken for pre-recruits to enter the fishable biomass is approximately one year. Fishery-independent surveys also support recent increases in PRI. Model outputs indicate considerable increases in legal-size biomass over the last three seasons. In 2019, the estimate was approximately 4,235 t, equating to an exploitation rate of 29%, the lowest on record Despite recent increases, egg production in the fishery remains low with 2019 estimates equating to 12% of unfished levels. In 2019, the CPUE of 1.59 kg/potlift was above the TrRP of 0.60 kg/potlift. Asa result, the SZRLF stock is classified as "sustainable". This means that the current fishing mortality is being adequately controlled to avoid the stock becoming recruitment impaired.