Using bioeconomic modeling to improve a harvest strategy for a quota-based lobster fishery

In Australian fisheries, explicit harvest control rules are increasingly applied to achieve bioeconomic objectives. Enhancing economic return, an objective valued by both regional communities and the fishing industry, can often be achieved by increasing stock abundance, consequently supporting the second principal management objective of sustainability. A harvest strategy proposed by the fishing industry for the Southern Zone rock lobster fishery in South Australia implemented in 2011 was based on a table that, given CPUE from the preceding season, specified the following year's catch quota (total allowable commercial catch, TACC). A guiding principle in constructing the 2011 harvest control rule was to target a constant exploitation rate. Here we report on bioeconomic modeling undertaken to evaluate and improve this harvest strategy. A length-based stock assessment model was extended to forward project biological and economic time series to evaluate candidate harvest strategies. Key performance indicators were the 10-year projected discounted profit, biomass, egg production and catch stability. These simulations imply that the 2011 harvest strategy required only moderate change: (1) current or moderately lower levels of exploitation are economically optimal; (2) narrower CPUE band widths for the TACC-vs-CPUE decision rule table enhance yearly catch stability; and (3) for depressed levels of stock abundance, exploitation rates were set to decrease linearly down to a lower limit reference point of CPUE below which the fishery is closed. A final harvest strategy incorporating these features was adopted in 2014 for yearly quota setting.