Assessing alternative management strategies for blacklip abalone

Unsustainability of abalone harvesting has become a worldwide trend. Australian abalone fisheries have thus far defied this seemingly inevitable path towards collapse, remaining generally sustainable until recently. Today unfavourable market and export conditions, disease, climate change, ecological shifts, and reduced catch quotas challenge the capacity of Australian abalone fisheries to remain sustainable into the future. Profits are down and the resilience of these fisheries is under threat. The two major stakeholders of the Australian abalone fishing industry are the commercial license owners and the government. The licence owner's goal is to maximise their annual catch whilst the main responsibility of government is to ensure the continued health of the fishery. In the early decades of the fishery both goals were relatively easily satisfied, however recent times have seen increased conflict between the two parties. Government is obliged to strongly consider the livelihoods of the licence owners whenever it applies annual changes to commercial harvesting strategies. However, it is faced with increasingly difficult decisions as abalone populations spiral into decline. Management of abalone fisheries has proved to be an onerous task over many decades. Abalone live near the shoreline and can be found down to 30 metres depth. Their populations from one reef to the next are as unpredictable as the rocky reefs they inhabit. Whilst many abalone are visible on the outer surface of a complex boulder system, it is difficult to accurately predict how many are hidden in inaccessible cracks and crevices. Initially, fishery assessment modelling of abalone populations took place at a management zone level covering hundreds of kilometres of coastline. Due to recent factors such as population collapse from overfishing and disease, causing reduction of harvesting quotas, abalone biomass modelling is now performed at a finer regional level scale (a few kilometres of coastline). Single reefs, which provide a few tonnes of commercial catch annually, are now monitored in isolation. Due to the expensive nature of fishery independent sampling, most reefs rely primarily on the previous annual catch as the feedback source. Regular workshop meetings are a secondary feedback source, where diver observations at each reef are recorded. CPUE (catch per unit of effort) has been dismissed as having low efficacy in abalone fisheries due to divers' abilities to target multiple abalone aggregations efficiently, whilst the fishery is reasonably abundant. However, the importance of measuring effort from a modelling perspective is critical, when finding the tipping point, at which time a reef becomes unfishable due to scarcity of legal sized abalone. This study explores the contrast between current management strategies and alternative management strategies incorporating indexes such as average length of commercial catch (ALCC) as a feedback. A central question in this process is; which management strategy is most likely to recover a vulnerable population, ensuring a robust biomass producing stable harvest rates? An existing Abalone model is used to test several harvest management strategies on a regional population of blacklip abalone, Halitois rubra. A high-mortality event is contrived early in the test phase, to simulate a disease sweeping through the population. To assess long-term sustainability of the population, mean values of cumulative yield, total biomass and legal biomass are estimated at the conclusion of a simulation period. An average length of commercial catch (ALCC) strategy provided the longest-term sustainability, in the form of protection to legal biomass, for a population subjected to significant stock loss. However, the slow nature of harvest recovery under the ALCC strategy meant the existing harvesting strategy is the most economically viable strategy for our population recovery. Despite this finding, the abalone industry would benefit greatly by investing effort, measuring shell lengths among commercial catches at fine scales. These data would provide information resulting in greater protection to individual populations via the setting of appropriate legal minimum lengths.