Rescaling of the daily/monthly nominal Tristan CPUE to make it comparable with the target CPUE level (Itar) used in the OMP.

The MARAM document MARAM/Tristan/2016/MAY/08 provides the full details of the updated (and rescaled) Tristan GLM-standardised lobster CPUE analysis. From the results presented in this document, the most recent target level for Tristan has been calculated.

Ovenstones receive electronic logbook updates of the powerboat fishing at Tristan on a daily basis, and this has been used to calculate the daily CPUE rates to compare them with previous seasons as well as the target CPUE level. Whilst this information is not what is used as input to the OMP, it is useful to be able to assess the performance of the fishery in real time.

There is a problem however with just considering the simple nominal CPUEs (at a daily or monthly level) when comparing them to the target CPUE, as the nominal CPUE values do not take important factors such as the monthly variation in CPUE into account. The CPUE target is an “annual” target level – but due to monthly natural variations in CPUE performance, the target thus in reality varies between months.

This document briefly outlines the steps suggested in re-scaling the daily CPUE values so that they will be comparable with the target CPUE value.