Alonzo and Mangel: Sex-change rules, stock dynamics, and the performance of spawning-per-recruit measures in protogynous stocks 239 



0.5 



1.5 



2.5 



800 



600 



400 



200 ' 







B Rule 2: Relative size 



0.5 1 15 



C Rule 3: Relative frequency 



2.5 



S 800 



L,=30r=1 



0.5 



1.5 



2.5 



D Rule 4: Reproductive success 



2.5 



Fishing mortality 



Lj=35 r=1 

 "77=30 r=1 



L,=25 r=1 



L,=35 r=1 



Figure 4 



The effect of size-selective fishing on the predicted mean population 

 size 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 L^— 30 and r=0.1 because the population is predicted to 

 crash at any fishing mortality in this scenario. 



Yet, the exact response depends greatly on the specific 

 pattern of sex change. For example, the population sex 

 ratio is not predicted to change much in the presence of 

 fishing when sex change is based on expected reproduc- 

 tive success and fishing pattern has little effect on the 

 sex ratio (Fig. 5). However, when sex change is based on 

 expected reproductive success, the annual yield is greater 

 for fishing patterns with larger size thresholds (Fig. 6). In 

 contrast, when sex change is determined by the mean size 



of individuals at the mating site, sex ratio is predicted 

 to increase with fishing and increase more when smaller 

 size classes are fished. However, for this pattern of sex 

 change, the smallest size threshold is also predicted to 

 lead to the largest yield of the fishery, although as fishing 

 mortality increases the difference between fishing pat- 

 terns with differing size thresholds decreases. Therefore, 

 the fishing pattern that will produce optimal yield will 

 depend on the exact pattern of sex change (Fig. 6). 



