Abstract
Variations in biomass during the last 4 months at sea are shown, using either the estimates of growth and natural mortality given by T. Doi, or other, hypothetical estimates. Based on Doi''s description, biomass from 1-2 months before return is 4% greater than after return to inshore waters. However, under present conditions of exploitation (4 months offshore fishing with dropout, i.e. fatal interception of fish without capture, and an additional harvest of 50% of the inshore return) the combined yields are likely to be lower than inshore yields with prior offshore fishing absent. Doi''s index of rationality of offshore fishing is examined and compared with index numbers obtained when yields are expressed in units of harvestable excess over specific levels of spawner requirement.

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