Summary of proportional recruitment and multiyear biomass variability for krill in Subarea 48 from research surveys

This document summarizes several papers submitted to the Grym e-group and other working groups during 2020 and 2021 on proportional recruitment (R.mean, R.var inputs to the Grym: the square of SD of proportional recruitment is the 'R.var' input) from research surveys and the fishery; and biomass variability (B0logsd input to Grym) from research surveys in Subarea 48. Two different length ranges, <36 mm and <40 mm, are used to define 'recruits' in the proportional recruitment comparisons. Proportional recruitments calculated from the fishery samples were generally lower (mean range 0.083 to 0.405, SD range 0.109 to 0.213) than the means and standard deviations from the survey data (mean range 0.174 to 0.579, SD range 0.274 to 0.412) for the two length values used to define recruits. This may be the result of the fishery targeting specific size ranges instead of random sampling of the annual size distributions for krill. Using the AMLR data aggregated over all areas and years, proportional recruitment mean and standard deviation were 0.219 and 0.320, respectively, if krill < 36 mm are defined as recruits, and 0.303 and 0.358, respectively, if krill < 40mm are defined as recruits. The mean of the annual CVs for Subarea 48.1 was 0.399, for a mean B0logsd of 0.384. The mean annual CV for Subarea 48.3 was 0.373, for a mean B0logsd of 0.361. Biomass CVs for Subareas 48.1 and 48.3 combined ranged from 0.086 to 1.15. B0logsd values for the combined Subareas ranged from 0.086 to 0.918 with a midpoint of 0.502.