Alternative proportional recruitment estimates for Subarea 48.1 based on reanalysis of the US AMLR data series

Assessment of the Precautionary Harvest Rate (Gamma) for the Antarctic krill in Subarea 48.1 was still to be finalized largely due to the proportional recruitment parameters which are key inputs of the Grym. The current mostly discussed proportional recruitment parameter estimates were based on the entire US AMLR summer survey time series but with data collected in DAYTIME only. However, two concerns may arise from such usages of the data. Firstly, it has been recommended to use data collected at night only to reduce the light-linked net avoidance of krill; secondly, the Joinville Island stratum, which has been recognized as an important area for krill recruits, was not fully covered by the entire US AMLR survey time series. In this paper, we provide alternative proportional recruitment estimates based on re-analysis of the US AMLR data given the above two considerations, resulting in an Gamma estimate of 0.0355 based on the 2002-2011 continuous time series and an Gama estimate of 0.0412 based on all surveys (2002-2011 plus 1997) that covered the all 4 US survey stratum using data collected at night only.