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Fishery Bulletin 93(4). 1995 



ratio of a population, however, will depend on the 

 mechanisms controlling sex reversal. For example, 

 for protogynous populations, if female to male sex 

 change is determined by size or age, a decline in the 

 proportion of males will be expected. Such effects 

 have been reported by Thompson and Munro (1983) 

 in comparing populations of serranids subjected to 

 different levels of fishing pressure in the Caribbean. 

 In contrast, no fishing-related effects were detected 

 by Reeson (1983) on populations of scarids. Social 

 induction of sex change is known or claimed for many 

 species offish (Shapiro, 1987). If this is the case, se- 

 lective removal of larger individuals would induce 

 female to male sex change, compensating for the ef- 

 fects of fishing on the sex ratio. Consequently, a re- 

 duction in the average size and age of sex change 

 would be expected. 



A widely recognized management strategy in the 

 conservation of reefs is the implementation of ma- 

 rine fisheries reserves, areas designed to protect 

 stocks of reef fish and habitats from all forms of ex- 

 ploitation (PDT, 1990; Williams and Russ, 1994). The 

 first marine protected area was established in Florida 

 in 1930. Since then, protected marine areas have 

 been implemented all over the world (PDT, 1990). In 

 Australia, the first protected marine areas were es- 

 tablished in the Capricornia Section of the Great 

 Barrier Reef Marine Park in 1981, under the first 

 zoning plan to come into operation (Craik, 1989). 



Evidence suggests that long-term spatial closure 

 to fishing increases the density, biomass, average 

 size, and fecundity of reef fishes (see PDT, 1990; Russ, 

 1991; Russ et al., in press, for reviews, but see 

 DeMartini, 1993). Furthermore, by enabling popu- 

 lations of reef fishes to attain or maintain natural 

 levels, marine reserves have been suggested as a 

 means to help maintain or even enhance yields of 

 fishes from areas adjacent to the reserves (Russ, 

 1985; Alcala and Russ, 1990). 



The spatial structure of coral reefs provides an 

 excellent opportunity to test for the effects of differ- 

 ent management alternatives (Hilborn and Walters, 

 1992). The importance of experimental investigations 

 on the effects of fishing on coral reefs that are used 

 as replicate experimental units has been pointed out 

 by various authors (Russ, 1991; Hilborn and Walters, 

 1992; Walters and Sainsbury 1 ). Yet, in spite of the 

 high expectations placed on marine reserves, few 

 direct tests exist on the effects of such protection on 

 yields of marine resources (Alcala and Russ, 1990). 



The leopard coralgrouper (also known as "coral 

 trout"), Plectropomus leopardus, is a long-lived, 

 protogynous hermaphroditic fish that represents a 

 very important fishery resource over the Great Bar- 

 rier Reef, Australia. With approximately 1,200 tonnes 

 caught annually, the leopard coralgrouper is the larg- 

 est single component in the annual commercial catch 

 of Queensland line-fishing (Trainor, 1991). Because 

 of its importance, the leopard coralgrouper has been 

 the subject of many studies on the effects of fishing. 

 These studies have compared the abundance and size 

 structure of populations from open and closed reefs 

 on the Great Barrier Reef (see Williams and Russ, 

 1994, for review). Most of these studies were con- 

 ducted by using underwater visual census (UVC) 

 techniques. Increased average size of the leopard 

 coralgrouper on reefs closed to fishing was detected 

 in most cases (Craik, 1981; Ayling and Ayling 2 ' 3 ; 

 Ayling and Mapstone 4 ). Beinssen 5 used UVC, line 

 fishing, and mark-release-recapture techniques to 

 investigate the effects of a 3.5 year closure on Boult 

 Reef and detected a significant increase in average 

 size of leopard coralgrouper. The same reef was sub- 

 sequently opened to fishing and after 18 months a 

 significant decrease in the average size of leopard 

 coralgrouper was detected (Beinssen 5 ). No study, 

 however, has investigated the effects of fishing on 

 the age and sex structure of leopard coralgrouper 

 populations. The age and growth of Plectropomus 

 leopardus has been recently validated (Ferreira and 

 Russ, 1994), making it possible to use age as an indi- 

 cator of changes in population structure under dif- 

 ferent levels of fishing pressure and through time. 



In 1987 a zoning plan was established in the cen- 

 tral section of the Great Barrier Reef Marine Park, 

 Australia, dividing the area into zones that allowed 

 different activities. Under this plan, fishing was ex- 

 cluded from some areas. In this study, samples taken 

 from reefs in the central section of the Great Barrier 

 Reef located in areas closed to fishing (National Park 

 Zones) since 1987, are compared with samples taken 

 from reefs located in areas open to fishing (General 

 Use Zones). The effects of this 3-4 year closure on 



1 Walters, C, and K. Sainsbury. 1990. Design of a large scale 

 experiment for measuring effects of fishing on the Great Bar- 

 rier Reef. Unpubl. Rep. to the Great Barrier Reef Marine Park 

 Authority (GBRMPA), Australia, 47 p. 



2 Ayling, A. M., and A. L. Ayling. 1984. A biological survey of 

 selected reefs in the Capricorn section of the Great Barrier Reef 

 Marine Park. Unpubl. Rep. to GBRMPA, Australia, 25 p. 



3 Alying, A. M., and A. L. Ayling. 1986. A biological survey of 

 selected reefs in the Capricorn section of the Great Barrier Reef 

 Marine Park. Unpubl. Rep. to GBRMPA, Australia, 25 p. 



4 Ayling, A. M„ and B. P. Mapstone. 1991. Unpubl. data col- 

 lected for GBRMPA from a biological survey of reefs in the 

 Cairns section of the Great Barrier Reef Marine Park. Unpubl. 

 Rep. to GBRMPA, Australia, 30 p. 



5 Beinssen, K. 1989. Results of the Boult Reef replenishment 

 area study. Rep. to GBRMPA, Australia, 28 p. 



