Marine park monitoring informs productivity potential of a southern rock lobster resource in South Australia

Abstract The Neptune Islands Group and Western Kangaroo Island Marine Parks were declared as part of South Australia’s representative system of Marine protected areas (MPAs) in 2009. Sanctuary zones, located within these MPAs, prohibited commercial fishing in the state’s Northern Zone Rock Lobster Fishery from 2014. In 2022, dedicated surveys were undertaken both inside and outside two of the sanctuary zones to estimate the relative abundance (catch per unit effort; CPUE) and size of southern rock lobster ( Jasus edwardsii ). Survey results were then compared to estimates of abundance obtained from long-term commercial fishery-dependent data within each area. The legal-size CPUE by weight of lobsters was 389% and 411% higher inside sanctuary zones of the Neptune Islands Group and Western Kangaroo Island, respectively, compared to outside, based on survey data. Survey catch rates inside the two sanctuary zones were also considerably higher than historical catch rates estimated from commercial fishing data. Lobsters inside both sanctuary zones were larger than those outside in terms of mean weight compared to historical estimates. However, surveys recorded similar mean size in lobsters both inside and outside the Neptune Islands Group sanctuary zone, indicating a possible spillover effect of MPA protection. The Northern Zone Rock Lobster Fishery is currently in a biomass rebuilding phase. The results highlight the productivity potential of temperate reef ecosystems within South Australia in terms of southern rock lobster abundances.