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Nightingale island rock lobster assessment updated for 2020

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This paper provides an updated assessment of the rock lobster resource at Nightingale island. This assessment includes updated data from both the commercial fishery and the biomass surveys. The recent (2013+) high GLM standardised CPUE values (and biomass survey index values) at the island, which were not anticipated earlier, suggest that the possible negative impact of the OLIVA incident on adults may have been overestimated previously and that the associated additional mortality was much less than originally assumed. The 2020 Reference Case (RC) assessment assumes zero adult mortality in 2011 due to the OLIVA incident, but continues to assume an associated additional 80% juvenile mortality. Results indicate that juvenile mortality following the OLIVA incident is likely to have been much less than this RC assumption. The current spawning biomass is estimated to be at a healthy 75%-87% of its pristine level. It is proposed that the RC be revised to assume an OLIVA-associated additional juvenile mortality reduced to 20%.



Department of Mathematics and Applied Mathematics, University of Cape Town