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Further test fishing analyses for Nightingale Island

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Because there was no pre-OLIVA fishing in the month of January 2011, the simpler earlier approach of Johnston (2011) to analyse test fishing data by month to assess the OLIVA impact needs to be refined to be able to include data from January 2012. General Linear Models are used for this purpose; these have the additional advantage that they can take more data into account in adjusting for monthly patterns. These models also reveal a regional pattern in the OLIVA impact, which is least in the north and greatest in the southeast. There is some indication that the impact has decreased slightly over time, but the trend is not statistically significant. The best estimate obtained for the OLIVA impact is a decrease of about 50% (SE=5%) in abundance of lobsters above the size limit.

When test fishing data over the July-October 2012 period are added there is clear evidence of a substantial increase in CPUE under test fishing in the 2012 compared to the 2011 season; discussion aimed towards the development of hypotheses to explain this would be desirable.



Department of Mathematics and Applied Mathematics, University of Cape Town