Legault and Ehrhardt: Correcting annual catches from seasonal fisheries for use in virtual population analysis 
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Figure 1 
Monthly catches from a total catch of 5,000 fish, given an initial population of 
10,000, under a seasonal fishery and under a constant fishing mortality rate (top 
panel). The resulting population decline by month under the two conditions is 
shown in the lower panel. 
bias caused by seasonal fisheries was made by 
MacCall (1986) who provided a family of approxima- 
tions to virtual population analysis based on Pope’s 
( 1972) cohort analysis. Hiramatsu ( 1995) generalized 
the equations to allow for a constant catch rate within 
a season, and Mertz and Myers (1996) reformulated 
the equations to allow for any seasonal pattern of 
catches. Most current software available for virtual 
population analysis and other age-structured analy- 
ses are designed for constant fishing mortality rates 
and annual time steps, however. Reformulating the 
basic equations used in virtual population analysis 
may not be practical for situations where a given al- 
gorithm is used that is already quite complex. 
An alternative to changing the time scale or modi- 
fying the equations for the analysis of a seasonal fish- 
