Alonzo and Mangel: Sex-change rules, stock dynamics, and the performance of spawning-per-recruit measures in protogynous stocks 241 



OJ 



A Rule 1: Fixed 



L,30r=1 



L,=35r=1 



L,=25 r=1 



5 1 1.5 



B Rule 2 Relative size 



25 



Z.,=25r=1 



L,=30 r=1 



L,=35 r=1 



L,=30r=0.1 



0.5 1 15 



(_> Rule 3: Relative frequency 



— i — 

 2.5 



L,=30r=1 



L,=35r=1 



L,=25 r=1 



D Rule 4: Reproductive success 



35 r=1 



1.5 2 



Fishing mortality 



Figure 6 



The effect of size-selective fishing on the predicted annual yield for 

 all four patterns of sex change. We present results for a sex-changing 

 stock with one mating site. Means across 20 simulations are given. For 

 details see text. The same basic patterns are predicted with multiple 

 mating sites. A line is not shown in panel A (when sex change is fixed) 

 where Zy=30 and r = 0.1 because the population is predicted to crash at 

 any fishing mortality in this scenario. 



spawning per recruit measures based on egg produc- 

 tion or fecundity could accurately assess the status 

 of sex-changing stocks. Although the fixed pattern of 

 sex change is predicted to show the greatest difference 

 between egg production per recruit and fertilized eggs 

 produced per recruit, each population shows deviations 

 between egg production and the production of fertilized 

 eggs. Thus egg production alone cannot tell us how 

 the population is being affected by fishing and classic 



SPR measures based on population fecundity may be 

 misleading for sex-changing stocks in cases where the 

 sex-change rule is not completely compensatory (rules 

 1-3). It is also interesting to ask whether consistent 

 differences exist (as has been suggested) in the resil- 

 iency of sex-changing stocks, compared to stocks with 

 separate sexes. Our results indicate that sex change 

 based on expected reproductive success is predicted to 

 have very similar dynamics to the dioecious population, 



