236 



Fishery Bulletin 103(2) 



E 

 o 



20,000 



16.000 



12,000 



8,000 



4.000 



5 



1 



1.5 



2.5 



B Rule 2: Relative size 

 \ 



05 



1.5 



2.5 



20,000 -X 

 16,000 ' 

 12,000 

 8,000 

 4,000 H 



C Rule 3: Relative frequency 



0.5 



1.5 



2.5 



20,000 



16,000 



12,000  



8,000 • 



4.000 







l) Rule 4: Reproductive success 



5 1 1.5 2 



Fishing mortality (F) 



25 



Figure 2 



The predicted effect of fishing mortality on the spawning stock biomass 

 per male recruit (dashed lines) and per female recruit (solid lines) for all 

 four patterns of sex change. Results are shown for the case of one mating 

 group and the fishing selectivity is characterized by L^=30 and r=l. The 

 same basic pattern is predicted for multiple mating sites as well. 



the strongest effect is predicted when size at sex change 

 is fixed or determined by the frequency of small fish in 

 the population (Fig. 3, A and C). When the size at sex 

 change is fixed, populations are predicted to crash when 

 mating sites are very small (Fig. 3A). In the case where 

 size at sex change is determined by expected reproduc- 

 tive success, group size is predicted to have no effect on 

 the relative production of eggs and mean population size 

 (Fig. 3D). However, for all the other rules of sex change 

 considered, smaller mating sites are predicted to experi- 

 ence sperm limitation in the presence of fishing, lead- 

 ing to a decrease in the relative production of fertilized 



eggs and a decrease in mean population size (Fig. 3). 

 However, unlike in the case of fixed size at sex change, 

 the smaller mating groups (20 mating sites with up to 

 50 individuals per site) are stable both in the presence 

 and absence of fishing and are not predicted to collapse 

 for most fishing patterns. 



Sensitivity to fishing pattern 



Rule 1 The size-selective pattern of the fishery has a 

 large effect on the predicted stock dynamics when the 

 size at sex change is fixed. When the selectivity of the 



