Abstract— Fisheries models have tradi- 

 tionally focused on patterns of growth, 

 fecundity, and survival offish. However, 

 reproductive rates are the outcome of 

 a variety of interconnected factors 

 such as life-history strategies, mating 

 patterns, population sex ratio, social 

 interactions, and individual fecundity 

 and fertility. Behaviorally appropriate 

 models are necessary to understand 

 stock dynamics and predict the success 

 of management strategies. Protogynous 

 sex-changing fish present a challenge 

 for management because size-selective 

 fisheries can drastically reduce repro- 

 ductive rates. We present a general 

 framework using an individual-based 

 simulation model to determine the 

 effect, of life-history pattern, sperm 

 production, mating system, and man- 

 agement strategy on stock dynamics. 

 We apply this general approach to the 

 specific question of how size-selective 

 fisheries that remove mainly males 

 will impact the stock dynamics of a 

 protogynous population with fixed 

 sex change compared to an otherwise 

 identical dioecious population. In 

 this dioecious population, we kept all 

 aspects of the stock constant except 

 for the pattern of sex determination 

 (i.e. whether the species changes sex 

 or is dioecious). Protogynous stocks 

 with fixed sex change are predicted to 

 be very sensitive to the size-selective 

 fishing pattern. If all male size classes 

 are fished, protogynous populations are 

 predicted to crash even at relatively low 

 fishing mortality. When some male size 

 classes escape fishing, we predict that 

 the mean population size of sex-chang- 

 ing stocks will decrease proportionally 

 less than the mean population size of 

 dioecious species experiencing the same 

 fishing mortality. For protogynous spe- 

 cies, spawning-per-recruit measures 

 that ignore fertilization rates are not 

 good indicators of the impact of fishing 

 on the population. Decreased mating 

 aggregation size is predicted to lead to 

 an increased effect of sperm limitation 

 at constant fishing mortality and effort. 

 Marine protected areas have the poten- 

 tial to mitigate some effects of fishing 

 on sperm limitation in sex-changing 

 populations. 



Manuscript approved for publication 

 23 July 2003 by Scientific Editor. 



Manuscript received 20 October 2003 

 at NMFS Scientific Publications Office. 



Fish. Bull 102:1-13(2004). 



The effects of size-selective fisheries 



on the stock dynamics of and sperm limitation 



in sex-changing fish 



Suzanne H. Aionzo 



Institute of Marine Sciences and the Center lor Stock Assessment Research (CSTAR) 



University of California Santa Cruz 



1156 High Street 



Santa Cruz, California 95064 



E-mail address shalonzoiS'ucscedu 



Marc Mangel 



Department of Applied Mathematics and Statistics 



Jack Baskin School of Engineering and the Center for Stock Assessment Research (CSTAR) 



University of California Santa Cruz 



1156 High Street 



Santa Cruz, California 95064 



Fisheries models are generally used 

 to predict the impact of fishing on 

 stock dynamics and yield (Quinn and 

 Deriso, 1999; Haddon, 2001). Classic 

 models have focused mainly on growth, 

 fecundity, and survival of species, with- 

 out considering the impact of mating 

 patterns on reproduction, survival, 

 and recruitment. It is now recognized 

 that life-history strategies and mating 

 behavior will affect stock dynamics. 

 Even so, general quantitative predic- 

 tions regarding the effect of specific 

 life-history patterns on fished popula- 

 tions are limited and further theory is 

 needed (Levin and Grimes. 2002). It 

 is likely that management strategies 

 taking into account a species' reproduc- 

 tive behavior will greatly improve our 

 ability to manage stocks (e.g. Beets and 

 Friedlander, 1999). We would also like 

 to know when the mating behavior and 

 reproductive strategies of a stock will 

 be worth investigating and when tradi- 

 tional management techniques will be 

 sufficient. For example, in a manage- 

 ment context, how do sex-changing 

 stocks differ from separate-sex species? 

 Here, we take an initial step toward 

 generating a theory of the combined 

 effect of life history and mating pat- 

 terns on stock dynamics by focusing 

 on the potential for and effect of sperm 

 limitation in a protogynous (female to 

 male) sex-changing stock. We focus 

 on protogyny for this article because 



numerous protogynous species are com- 

 mercially important, namely red porgy 

 {Pagrus pagrus), gag grouper iMyc- 

 teroperca microlepis), and California 

 sheephead iSemicossyphus pulcher). 



Sex-changing fish present a unique 

 challenge for management because size- 

 selective fisheries have the potential to 

 drastically reduce reproductive rates 

 and population size at levels of fishing 

 that would not pose a problem for dioe- 

 cious (separate-sex) species (Huntsman 

 and Schaaf, 1994; Armsworth, 2001; Fu 

 et al., 2001). On the other hand, pro- 

 togynous stocks may be less sensitive 

 to the removal of large individuals if 

 females are not fished and fertilization 

 rates remain high. Many commercially 

 important species are known to change 

 sex (Bannerot et al., 1987; Shapiro, 

 1987; Coleman et al., 1996; Brule et al., 

 1999; Adams et al., 2000; Armsworth, 

 2001; Fu et al., 2001). Previous models 

 have shown that sex-changing fish may 

 be vulnerable to fishing (Bannerot et 

 al., 1987; Huntsman and Schaaf, 1994; 

 Armsworth, 2001; Fu et al.. 2001). 



Complications arise because the ef- 

 fect of fishing on a sex-changing spe- 

 cies is mediated by many aspects of 

 their reproductive biology, such as sex 

 ratio, size-dependent fecundity, spawn- 

 ing aggregation size, and reproductive 

 skew. Furthermore, patterns of sex 

 change have cascading effects on the 

 sex ratio, social interactions, population 



