238 



Fishery Bulletin 103(2) 



A Rule 1: Fixed 



o> o 



a. 1.0 



ft 0.8 



15 Rule 2: Relative size 



Egg production Fert. egg production Mean population 

 per recruit per recruit size 



1.0 



08 



06 



0.4 



02- 



C Rule 3: Relative frequency 



D Rule 4: Reproductive success 



en £ 2 



Egg production Fert. egg production Mean population 

 per recruit per recruit size 



Figure 3 



Effects of mating group size on the response of egg production per recruit, fertilized egg production per recruit, and mean 

 population size to fishing pressure. Large (one large mating aggregation), medium 1 10 medium-sized mating aggrega- 

 tions) and small (20 small mating aggregations) situations are compared. Percent change in the presence of fishing (from 

 F =0 to F=l) is given. Total population fecundity and mean body size are lower for smaller mating aggregations as well. 

 Results are shown for Z^— 30 and r=l. No bars are shown for small mating groups with fixed size at sex change because 

 these populations are predicted to crash. 



Rule 4 As with all of the other patterns of sex change, 

 populations with sex change based on expected reproduc- 

 tive success are predicted to crash whenever small fish 

 experience fishing mortality (r=0.1, Fig. 4D). Further- 

 more, as with the other two plastic sex change rules, 

 populations are predicted not to crash when fish below 

 the normal mean size at sex change are included in the 

 fishery because the population can compensate with 

 smaller sizes at sex change in the presence of fishing 

 (Fig. 4D). Although only small differences among fish- 

 ing patterns are predicted in the mean population sex 

 ratio, the effect on the population size is predicted to be 

 greatest when many size classes are fished, and large 

 differences are predicted between the fishing patterns in 

 mean population size (Fig. 5D). Finally, in the scenario 

 of sex change based on expected reproductive success. 



the fishing pattern predicted to lead to the greatest catch 

 is to target only fish above the normal mean size at sex 

 change (1^=35, Fig. 6D). 



In summary, fishing is always predicted to decrease 

 total production of fertilized eggs and mean population 

 size. However, the strength of the effect depends both 

 on fishing selectivity and the pattern of sex change (see 

 above and Figs. 4-6). Although populations with fixed 

 patterns of sex change are predicted to crash in the pres- 

 ence of fishing below the mean size at sex change, plastic 

 patterns of sex change are predicted to lead to more 

 resilience since these populations can compensate for 

 the removal of large males more effectively. However, 

 all scenarios are predicted to crash in the presence of 

 fishing across a broad range of size classes (when r=0.1) 

 even in completely compensatory patterns of sex change. 



