10 



Fishery Bulletin 102(1) 



fisheries management of a behaviorally and evolution- 

 ary reasonable life-history and sex-change pattern. We 

 based our assumptions and parameter values on patterns 

 observed in natural populations that have presumably 

 evolved given the life history tradeoffs and expected repro- 

 ductive success associated with these behaviors. However, 

 we made various assumptions that affect the predicted 

 patterns such as a fixed sex-change pattern, male mating 

 success proportional to sperm production, and a very resil- 

 ient recruitment function. Despite these assumptions, a 

 number of general patterns emerge. 



Life-history pattern is important but not sufficient 

 to predict stock dynamics 



In general, we predicted that a protogynous stock with 

 fixed sex change will respond to the same fishing pressure 



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 0.5  



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Protogynous 



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Dioecious 



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600,000- 

 500,000' 

 400,000- 

 300,000- 

 200,000- 

 100.000 



Protogynous 



Dioecious 



Figure 7 



The effect of marine reserves on protogynous and dioecious popula- 

 tions when fishing effort is decreased (case 1 1. 1 A) Percent change 

 in the presence of fishing CF=1) in the production of fertilized eggs 

 compared to in the absence of fishing. ( B) Annual biomass removed 

 by the fisheries varies with marine reserve and sex-change pat- 

 tern. Numbers shown are for 10 mating sites when F=l. 



differently than an otherwise identical dioecious stock. 

 Understanding the life history of the population is clearly 

 important to our understanding of stock dynamics. How- 

 ever, it is not possible to classify protogynous stocks simply 

 as more or less sensitive to fishing. The differences between 

 dioecious and sex-changing fish are relatively complex, and 

 it is not the case that one life history is expected to be more 

 or less vulnerable to fishing. Although the sex change and 

 fishing pattern are important, they must be seen in the 

 context of the mating system, reproductive behavior, and 

 population dynamics of the species. If no male size classes 

 escape fishing, then the sex-changing population will be 

 much more sensitive to fishing and may crash even at low 

 fishing mortality. When some male size classes escape fish- 

 ing, an identical dioecious stock is predicted to experience 

 a greater decrease in mean population size than the pro- 

 togynous population. However, the protogynous species is 

 predicted to be much more sensitive to mating aggre- 

 gation size and sperm limitation. Protogynous stocks 

 are predicted to benefit from marine protected areas 

 at high levels of fishing mortality where sperm limi- 

 tation is common at fished mating sites. In contrast, 

 the dioecious stock is predicted to derive a greater 

 benefit of marine reserves even at low fishing mortal- 

 ity because of the protection of large fecund females 

 ( Fig. 7 ). Although the sex-changing population is pre- 

 dicted to be less sensitive to fishing mortality overall, 

 it is clearly very important to understand the exact 

 details of the sex-change pattern and the size-selec- 

 tivity of fishing in relation to sex change. It will also 

 be important to understand the mating system and 

 patterns of fertilization success and sperm produc- 

 tion in males when managing a protogynous stock. 

 Given the sensitivity of the sex-changing stock to the 

 size-selective pattern of fishing, we recommend the 

 precautionary approach of keeping fishing mortality 

 sufficiently low so that some males of all size classes 

 always escape fishing (Fig. 4C). Clearly, protogynous 

 stocks cannot be managed as if they were dioecious. 



Sperm limitation and mating aggregation size affect 

 stock dynamics 



The removal of large males from the population can 

 cause sperm limitation, decreased fertilization rates, 

 and decreased population size even in a resilient spe- 

 cies with high sperm production. Sperm limitation 

 will increase as mating group size decreases. In the 

 present model, even small males produced relatively 

 large amounts of sperm. If males are removed, popu- 

 lations with lower sperm production are predicted to 

 be more sensitive to the removal of large fertile males. 

 Our assumption of fertilization rates determined by 

 total egg and sperm production per mating site will, 

 if anything, have underestimated the potential for 

 sperm limitation. Other mating systems and repro- 

 ductive behaviors could lead to greater sperm limita- 

 tion than predicted in our study For example, species 

 that have not evolved under sperm competition should 

 be more affected by the removal of large males than 



