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Fishery Bulletin 103(2) 



isolates the cause — fishing. Yet with any simulation 

 analysis, one must interpret results in light of model 

 assumptions. With our model maturity was assumed to 

 be a function of age, and the computation of selection dif- 

 ferentials were consequently focused to those on growth 

 traits and size. If maturity were considered a function 

 of size, it too would have been subject to a selection 

 differential. Changes in size or age at maturity have 

 been considered in other studies (Stokes and Blythe, 

 1993; Haugen and Vollestad, 2001; Olsen et al., 2004) 

 and are likely connected to growth parameters through 

 bioenergetic constraints. 



A central assumption is that somatic growth follows 

 the von Bertalanffy model. That model was chosen be- 

 cause of its successful track record (Chen et al., 1992; 

 Quinn and Deriso, 1999). Life-history characteristics 

 other than growth are assumed to follow life-history 

 invariant relationships. The invariants constrain bio- 

 logical parameters to values that represent an "average 

 stock." Of course, no stock is truly average, and there- 

 fore our sensitivity analyses incorporate considerable 

 deviation from life-history invariants. 



In our simulation, the largest selection differentials 

 occurred when the spawning or fishing seasons were 



