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Fishery Bulletin 93(4). 1995 



When immature males were pooled with mature 

 males for sex ratio calculations, the resulting sex 

 ratio was not significantly different among reefs. 

 Therefore, it appears that despite the differential 

 distribution of developmental stages in the popula- 

 tions, the same final female:male balance was 

 achieved. This result suggests that behavioral mecha- 

 nisms are probably contributing to the determina- 

 tion of the distribution of sexes in the populations of 

 leopard coralgrouper. It is possible that for the leop- 

 ard coralgrouper, sex change results from a combi- 

 nation of a developmental process, in which individu- 

 als are more susceptible to sex change as they grow 

 larger and older, and from a social process through 

 behaviorally induced stimuli. Genetic variability 

 would widen the range over which sex change can 

 occur and phenotypic plasticity would allow individu- 

 als to respond to different social structures. Manipu- 

 lative experiments are probably necessary to detect 

 the exact mechanisms determining the distribution 

 of sexes in leopard coralgrouper populations. 



Estimations of mortality rates are essential to fish- 

 ery management, and yet few studies have made 

 estimates of the rate of total mortality of coral reef 

 fishes (Russ, 1991). However, an important assump- 

 tion of catch curve analysis, one of the most com- 

 monly employed methods to estimate mortality 

 (Beverton and Holt, 1957), is that all age groups have 

 been recruited with the same abundance (Pauly, 

 1984). The present data represent a clear example 

 of the problems that can result from the presence of 

 strong recruitment pulses in calculating the total 

 mortality rate Z from age- or length-structured catch 

 curves. Because of a strong year class, estimates of 

 Z calculated from the right-hand slopes of the catch 

 curves would suggest very high mortality rates for 

 the two closed reefs, in contrast with much lower 

 mortality rates on the open reefs. Mortality estimates 

 drawn from the present data or from similar cases 

 where significant recruitment fluctuation is retained 

 in the age structure would be very imprecise. 



For the leopard coralgrouper, our results suggest 

 that the occurrence of strong interannual fluctua- 

 tions in recruitment were retained in the age struc- 

 ture. With recruitment as a major factor driving the 

 patterns of abundance, recovery of leopard coral grou- 

 per populations after closure to fishing may be largely 

 dependent on a good pulse of recruitment. Thus re- 

 coveries of populations after closure to fishing are 

 likely to be "events" rather than gradual "processes," 

 and recovery may be rapid or slow, depending on the 

 timing of closure with respect to the occurrence of a 

 very large year class. 



Differences in the age structure were more obvi- 

 ous than differences in the size structure between 



open and closed reefs. As the leopard coralgrouper is 

 a relatively slow-growing fish, differences in the size 

 structure of a population will take longer to become 

 evident than will differences in the age structure. 

 Additionally, owing to considerable variability in size 

 at age (Ferreira and Russ, 1994), recruitment fluc- 

 tuations may also pass unnoticed if size-structure 

 data alone are examined. The results presented here 

 indicate that age structure may be far more useful 

 than size structure for comparisons of fishing effects 

 on long-lived fishes such as Epinephelinae serranids. 

 Comparisons based solely on mean sizes of reefs open 

 to fishing with those closed to fishing may fail to 

 detect important differences. 



Marine fishery reserves are a management strat- 

 egy with excellent potential for maintaining high 

 abundances of reef fishes (Alcala and Russ, 1990). 

 However, to understand better the processes deter- 

 mining differences in abundance, it is important that 

 studies on the effects of closures to fishing on long- 

 lived species include examination of age structure. 

 Furthermore, such studies must replicate reefs, take 

 into account strong recruitment pulses that may 

 mask fishing effects, and consider the effects of strong 

 recruitment pulses when estimating mortality from 

 catch curves. 



Conclusion 



In this study we found 1 ) no significant differences 

 between the mean size and age of leopard coral- 

 grouper on open and closed reefs were detected (such 

 a result could have been a consequence of the design 

 constraints of this study, such as not accounting for 

 variability among replicate reefs, or the duration of 

 closure (3-4 years); 2) that there were no differences 

 in the overall sex ratio, despite observed differences 

 in the sex structure, suggesting social induction of 

 sex change; 3) that a strong recruitment pulse oc- 

 curred, an event that may be extremely important 

 in determining variation in abundance of leopard 

 coralgrouper, and therefore very relevant to the fish- 

 eries; and 4) that age structure is more useful than 

 size structure in detecting effects of fishing on leop- 

 ard coralgrouper, and, therefore, age determination 

 should be a routine component in the management 

 of leopard coralgrouper populations. 



Acknowledgments 



We are most grateful to the crew of recreational fish- 

 ermen who collected the samples for this experiment. 



