Fishery Bulletin 102(1) 



5-25% of the simulations as fishing mortality (F) increased 

 from to 1. The impact of mating group size on stock dynam- 

 ics is thus predicted to be nonlinear. A threshold mating 

 aggregation size appeared to exist below which sperm limi- 

 tation and reproductive failure become common. 



Spawning-per-recruit measures 



For size-selective fishing, the spawning stock biomass per 

 recruit of females is not predicted to decrease significantly 

 with increased fishing mortality as long as some male size 

 classes escape fishing (Lr>L v ). However, male biomass per 

 recruit and sperm production per recruit are both predicted 

 to decrease. Although egg production is not predicted to 



decrease with increasing size-selective fishing pressure, 

 the number of fertilized eggs is predicted to decrease. 

 When all male size classes are fished iL.>L c ), the stock 

 is predicted to crash and therefore clearly female biomass 

 and egg production are predicted to decrease with fishing 

 mortality. In general, the predicted decrease in mean popu- 

 lation size and reproduction is driven for the most part by 

 decreased sperm production and consequently a reduction 

 in the number of eggs fertilized per recruit. The relation- 

 ships between fishing pressure and the classic spawning- 

 per-recruit measures do not indicate the true effect that 

 fishing is predicted to have on the protogynous population 

 (Fig. 6). When L f >L c , female spawning stock biomass per 

 recruit and eggs produced per recruit showed almost no 

 effect of fishing on the population, even as mean 

 population size decreased. Because of the size-selec- 

 tive fishing pattern, total and male biomass per recruit 

 decreased with fishing mortality and decreasing mean 

 population size. However, male and total biomass per 

 recruit did not reflect the increased effect of fishing on 

 populations with smaller mating aggregations. The 

 production of fertilized eggs per recruit decreased with 

 increased fishing pressure and decreased more sharply 

 for smaller mating aggregations. Only the number of 

 fertilized eggs per recruit could assess the predicted 

 effect of fishing on the protogynous population. Thus, 

 classic SPR measures were predicted to fail in the 

 presence of sperm limitation to assess the impact of 

 fishing on a protogynous stock. 



Marine reserves and fishery management 



In the situation considered in this study, the pattern 

 of fishing is more important to stock dynamics than 

 the presence of marine reserves. We assumed a size- 

 selectivity that allowed on average 50% of individuals 

 of sex-changing size to escape the fishing gear. Thus, 

 although the sex ratio does increase (become more 

 female) by 20-40%, all males are not lost from the 

 population (when L f s.L t . and r=l ). If fishing selectivity 

 occurs at a smaller size, then the effects on the popula- 

 tion are predicted to be much greater and the protogy- 

 nous stock would suddenly become more affected than 

 the dioecious population. For example, at L^=25 cm the 

 protogynous stock is predicted to crash whenever F^l. 

 This occurs not because of a reduction in the produc- 

 tion of eggs but rather because of a failure to fertilize 

 the eggs produced by surviving females. When males 

 of all size classes are fished, populations can become 

 male limited and fertilization rates drop drastically. A 

 decrease in the production of fertilized eggs can lead to 

 a decrease in female biomass, but it is the removal of 

 males rather than females that causes this decline. 



When fishing effort is not redistributed after the 

 formation of a reserve, the impact of fishing on the 

 mean population size and SPR measures is predicted 

 to decrease (e.g. Fig. 7A). However, if fishing effort is 

 redistributed among unprotected areas, the benefit 

 of the reserves to the protogynous stock decreases 

 (Fig. 8A). Protecting some sites allows large males to 



