Shepherd and Idome Yield- and spawning biomass-per-recruit for Centropnstis striata 



335 



120 



100 



Q. 



0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 

 FISHING MORTALITY 



Figure 9 



Percentage of maximum potential spawning 

 biomass-per-recruit for black sea bass 

 Centropnstis striata under various fishing mor- 

 talities and lengths-at-first-capture (L ( l using 

 the distributed delay model with transitions 

 (dashed) and without transitions ( solid K 



0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 

 FISHING MORTALITY 



Figure 10 



SSB/R for black sea bass Centropristis striata 

 estimated under varying transition rates-at- 

 length (L, = 16 cm). Rates were increased 209r 

 within each length-group indicated. 



were based on a target %MSP, the presence or absence 

 of transition terms in the model would provide dra- 

 matically different interpretations. For instance, if the 

 target % MSP were 30% with an F=0.8, and L c =25 cm, 

 the non-transitional model would indicate the situa- 

 tion was below the target at 22%, whereas the transi- 

 tional model would place the current conditions above 

 the target at 34%. It would be critical that calculation 

 of SSB in the stock-recruitment relationship used for 

 development of a target SSB/R (and associated %MSP) 

 be made using a framework similar to calculation of 

 SSB/R. 



Beyond the issue of the model structure is the appro- 

 priateness of using spawning biomass models in general 

 for management of hermaphroditic fishes. The complex 

 social hierarchy of reef fishes (black sea bass can be 

 considered a temperate reef fish ) during spawning im- 

 plies that the number of males may be an important 

 factor limiting reproductive potential (Smith 1982). Re- 

 cent theoretical studies suggest that males are not limit- 

 ing in hermaphroditic sea bass populations to the degree 

 that non-dominant males participate in spawning 

 ("streakers") (Peterson 1991). If streakers are abundant, 

 there would be no benefit for a female to transform only 

 to engage in sperm competition with other spawning 

 males. This suggests that under limited exploitation, the 

 reproductive potential of the population is restricted in 



