Abstract. Samples of Plectro- 



pomus leopardus collected at two reefs 

 (Glow and Yankee) that have been 

 closed to fishing since 1987 were com- 

 pared with samples collected at two 

 reefs (Grub and Hopkinson) that were 

 open to fishing to investigate the effects 

 of a 3-4 year closure on the size, age, 

 and sex structure of leopard coral- 

 grouper (also known as "coral trout") 

 populations. There were no significant 

 differences in mean size and age be- 

 tween protected reefs and unprotected 

 reefs. However, mean size and age var- 

 ied significantly between the two pro- 

 tected and the two unprotected reefs. 

 In the two reefs closed to fishing, the 

 population structure was dominated by 

 the presence of a strong year class 

 which settled in early 1984, indicating 

 the occurrence of strong interannual 

 fluctuations in recruitment. A similar 

 pattern was not observed on the reefs 

 open to fishing, suggesting that fishing 

 mortality may have caused the de- 

 crease in abundance of this strong year 

 class on the open reefs. Sex change oc- 

 curred over a wide range of sizes and 

 ages on the four reefs. A comparison of 

 the frequency of developmental stages 

 between reefs indicated significant 

 variation. The two unprotected reefs 

 had a smaller proportion of males, but 

 that seemed to be compensated for by 

 a larger proportion of transitional-stage 

 fish and young males. Although the dis- 

 tribution of developmental stages in the 

 populations was different, the same fi- 

 nal female: male balance was achieved. 

 This suggests that for the leopard 

 coralgrouper, sex change results from 

 a combination of developmental and 

 behavioral processes. Differences in age 

 structure were more obvious than dif- 

 ferences in the size structure between 

 closed and open reefs, suggesting that 

 age structure may be far more useful 

 than size structure for comparisons of 

 fishing effects on long-lived fishes such 

 as Epinephelinae serranids. Compari- 

 sons of open and closed reefs based 

 solely on mean sizes may fail to detect 

 important differences. 



Population structure of the 

 leopard coralgrouper, 

 Plectropomus leopardus, on fished 

 and unfished reefs off Townsville, 

 Central Great Barrier Reef, Australia 



Beatrice R Ferreira 



Departamento de Oceanografia 

 Universidade Federal de Pernambuco 

 Recife-Pernambuco CEP 50.739-540, Brasil 



Garry R. Russ 



Department of Marine Biology 



James Cook University of North Queensland 



Townsville Q48 1 1 , Australia 



Manuscript accepted 24 April 1995. 

 Fishery Bulletin 93:629-642 ( 1995). 



Fishing is one of the most important 

 human exploitative activities on 

 coral reefs (Munro, 1983; Munro 

 and Williams, 1985; Russ, 1991). It 

 has been suggested that fishing 

 may have a greater impact upon 

 fish populations and communities 

 of coral reefs than upon those of 

 temperate seas because of the more 

 territorial nature of most coral reef 

 fish (Russ, 1991). Therefore, the 

 impact of fishing on populations and 

 communities of coral reef fishes has 

 been of considerable interest. Large 

 predatory species are especially af- 

 fected by overfishing owing to life 

 history characteristics such as slow 

 growth, high longevity, low rates of 

 natural mortality, and limited adult 

 mobility (Plan Development Team 

 [PTD], 1990; Russ, 1991). 



Fishing is known to cause selec- 

 tive removal of larger (and presum- 

 ably older) individuals, thus reduc- 

 ing their proportion in the popula- 

 tion (Ricker 1969; Miranda et al., 

 1987 ). Although evidence for effects 

 of fishing on the size structure of 

 populations of coral reef fishes is 

 strong (Munro, 1983; PDT, 1990), 

 there is little evidence for effects of 

 fishing on age structure, probably 



because of the perceived difficulties 

 in age determination of tropical 

 fishes (Manooch, 1987). On the 

 Great Barrier Reef, for example, 

 information on age structure from 

 a number of reefs exists for only one 

 species, the damselfish Poma- 

 centrus moluccensis (Doherty and 

 Fowler, 1994). In the presence of 

 high variability in size at age, in- 

 formation on age structure can 

 provide information on harvesting 

 effects not obtainable by size-struc- 

 tured data alone. Different growth 

 processes can also be associated 

 with selective fishing mortality 

 (Parma and Deriso, 1990), enhanc- 

 ing the importance of analyzing age 

 in assessments of the the effects of 

 fishing on such populations. 



Sequential hermaphroditism is 

 common among coral reef fishes 

 (Thresher, 1984). Bannerot et al. 

 (1987) modelled the resilience of 

 protogynous populations to exploi- 

 tation and concluded that a definite 

 risk existed in managing these 

 stocks by traditional yield-per-re- 

 cruit models under high fishing 

 pressure. The effects of selective 

 removal of larger individuals (pre- 

 sumably mostly males) on the sex 



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