Estimates are calculated for the parameter λ in the yield equation Y = λMB₀ for a krill fishery in which both the fishery and krill growth are seasonal. The criterion used for the calculations is that the probability that the krill spawning biomass drops below 20% of its median pre-exploitation level over a 20 year period of harvesting should equal 10%. The value of, λ depends strongly on the value of M (natural mortality) and σ_R (recruitment variability), and also on the relative values of the ages at maturity and first-capture. Seasonal effects seem to be of lesser importance.