An alternative method of calculating precautionary yield

Precautionary yield ('gamma', the proportion of stock biomass harvested annually) for the Antarctic krill fishery is currently chosen by comparing krill spawning stock biomass (SSB) during 20-year model projections to pre-exploitation spawning stock biomass (SSB0). Both SSB and SSB0 are simulated for these projections using input data considered known. Precautionary yield derived from an alternative calculation described here compares krill SSB during 20-year projections with and without fishing, identifying the effect of fishing instead of comparing SSB and SSB0. The alternative method appears to produce similar yields to the conventional calculations when recruitment variability is low, but higher yields than the conventional method when recruitment variability is high. In two examples of highly variable krill recruitment, precautionary yields increased from 0 using the current approach to 0.02 and 0.03.