Improving fleet efficiency to maximise economic yield in a Western Australian prawn fishery |
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| Institution: | 1. Institute of Exact and Technological Sciences-Federal University of Viçosa, Rodovia BR 354, km 310, P.O. Box 22, CEP 38810000 Rio Paranaíba, MG, Brazil;2. Institute of Mathematics and Computer Sciences, University of São Paulo, Av. Trabalhador São-Carlense, 400, CEP: 13560-970 São Carlos, SP, Brazil;3. College of Science and Engineering James Cook University, 1 James Cook Drive, Townsville QLD 4811, Australia |
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| Abstract: | The Shark Bay trawl fishery is Western Australia's most valuable prawn fishery (worth AUD$25 million in 2014). The 18-vessel fleet targets western king prawns (Penaeus latisulcatus), brown tiger prawns (P. esculentus) and also retains saucer scallops (Ylistrum balloti) and blue swimmer crabs (Portunus armatus). Increased fuel prices, falling prawn prices and lower catches of other species, following extreme environmental events, have impacted fishery profits. A biomass dynamics model with an economic component indicated that total revenue levels start to decline when annual effort increases beyond ~ 200 fishing days per boat. Annual effort required to achieve MEY, when based solely on prawn fishing, is 115–150 days per boat after accounting for fixed and variable fishing costs and annual fishing efficiency increases of 1–2%. From 2007–2014, the adjusted effort was 188–192 days per boat. Fishing occurred between March and November during 7–8 fishing periods, separated by 5–8 day (low catchability) moon closure periods. An empirical daily profit assessment (2007–2015), accounting for recruitment variation, daily prawn size compositions, monthly market prices for different prawn species and sizes, and daily fishing costs, showed vessels made profits on ~ 115–160 days and losses on ~ 15–55 days per year, when fishing occurred near the full moon. The fishery benefitted in 2013–2015 by starting later in the year and better targeting within-season effort. This management strategy within the effort-control framework, which improved profitability, maintained higher spawning stocks and reduced ecosystem fishing impacts, has wider application in prawn fishery management. |
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| Keywords: | Economic benefits Annual production model Fishing effort Daily profits Size composition Delayed fishing Maximum economic yield |
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