314 



Fishery Bulletin 94(2). 1996 



reefs within a single geographic area of the Great 

 Barrier Reef have been published for only two spe- 

 cies: the damselfishes Pomacentrus moluccensis and 

 P. wardi (Doherty and Fowler, 1994, a and b). A num- 

 ber of studies have compared the abundance and size 

 structure of the serranid Pleetropomus leopardus 

 between reefs open to fishing and those closed to fish- 

 j n g 4.5.6 jyj ore recently, Ferreira and Russ ( 1995) have 

 examined the size, age, and sex structure of popula- 

 tions of P. leopardus on closed and open reefs in the 

 central Great Barrier Reef region. 



The hussar, Lutjanus adetii, and the five-line snap- 

 per, L. quinquelineatus, are both widely distributed 

 along the entire length of the Great Barrier Reef 

 (10°S-24"S) and occur as far as 34"S (Kuiter, 1993). 

 The habitats of both species vary, although they are 

 most commonly associated with hard bottom areas. 

 In the central Great Barrier Reef region, L. adetii is 

 common at depths greater than 30 m within the 

 midshelf group of reefs and is known to occur on the 

 outershelf at depths up to at least 99 m, whereas L. 

 quinquelineatus is common in both shallow and deep 

 waters on both midshelf and outershelf reefs to a 

 depth of at least 128 m (Newman, 1995). Loubens 

 ( 1980) has demonstrated that both species are rela- 

 tively long lived and slow growing in New Caledonia; 

 similar conclusions have been obtained from the cen- 

 tral Great Barrier Reef (Newman et al. 7 ). 



Neither of these lutjanids forms a significant por- 

 tion of the commercial catch in the central Great 

 Barrier Reef, and they form only a nominal contri- 

 bution to the recreational catch in this region (Higgs, 

 1993; Newman, 1995). However, in the southern 

 Great Barrier Reef, L. adetii contributes a signifi- 

 cant proportion to the commercial lutjanid catch 

 (Newman, 1995) and may become of increasing sig- 

 nificance to the recreational line fishery in future 

 years. s Relatively little information is available con- 



1 Ayling, A. M., andA. L. Ayling. 1984. Distribution and abun- 

 dance of coral trout species (Plectropomus spp.l in the Swain 

 group of reefs. Capricorn section of the Great Barrier Reef Ma- 

 rine Park. Unpubl. report to the Great Barrier Reef Marine 

 Park Authority (GBRMPA; Project 171), Australia. 



5 Ayling, A. M., and A. L. Ayling. 1986. A biological survey of 

 selected reefs in the Capruornia section of the ( ireat Barrier Reef 

 Marine Park. Unpubl. report to the Great Barrier Reef Marine 

 Park Authority (GBRMPA; Project 243 and 269 1, Australia. 



K Ayling, A. M., and B. P. Mapstone. 1991. Unpublished data 

 collected for GBRMPA from a biological survey of reefs in the 

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

 report to the Great Barrier Reef Marine Park Authority 

 i GBRMPA I, Australia. 



7 Newman, S. J., D. McB. Williams, and G. R. Russ. Age valida- 

 tion, growth, and mortality rates of the tropical snappers (Pi- 

 sces Lutjamdaei. Lutjanus adetii (Castelnau, 1 873 1 and L. 

 quinquelineatus i Bloch, 17901 from the central Great Barrier 

 Reef, Australia. Submitted to Mar. Freshwater Res. 1 1996). 



cerning the ecology of these species in Australian 

 waters. 



The recent validation (Newman et al. 7 ) of age and 

 growth for both L. adetii and L. quinquelineatus has 

 facilitated the comparison of demographic param- 

 eters of both these species at the spatial scale of in- 

 dividual reefs. The aims of this study are to examine 

 spatial variability in growth, mortality, and age struc- 

 tures of populations of L. adetii and L. quin- 

 quelineatus among reefs within the central Great 

 Barrier Reef region (Fig. 1). 



Materials and methods 



Sampling procedures 



Specimens ofL. adetii in =355) and L. quinquelineatus 

 (n-573) were obtained between October 1991 and 

 December 1993 from fish traps (O-trap design with 

 40-mm galvanized hexagonal wire mesh | Newman, 

 1995]) used during a research program investigat- 

 ing the distribution and abundance of lutjanids among 

 reefs in the central Great Barrier Reef region ( Newman, 

 1995; Newman and Williams, 1995). Samples of both 

 species were obtained from four reefs (Rib |RI], John 

 Brewer |JB1, Lodestone [LO], and Kelso [KL]); addi- 

 tional samples of L. quinquelineatus were obtained from 

 two other reefs ( Davies [ DV] and Myrmidon I MR 1 1 ( Fig. 

 1). Individual L. adetii <17 cm fork length (FL) and L. 

 quinquelineatus <10 cm FL were usually not vulner- 

 able to trap fishing and specimens in this size range 

 were therefore not obtained for analysis. 



Individuals of each species were measured (FL and 

 standard length [SL]) and weighed (clean weight after 

 removal of the gills and viscera), and sexes were deter- 

 mined by macroscopic examination of the gonads. The 

 sagittal otoliths of individuals were removed and sec- 

 tioned laterally through the focus with a Beuhler Isomet 

 low-speed jewelry saw, and ages were determined ac- 

 cording to the methods described in Newman et al.' 



Analysis of data 



Because a previous study (Newman et al.') indicated 

 significant differential growth between sexes in both 

 species, two-way factorial analyses of variance were 

 used to compare the mean length (FL, mm), age 

 (years), and clean weight (g) of each species both 

 among reefs and between sexes (in order to prevent 



rt Williams, D. McB., and G. R. Russ. 1994. Review of data on 

 fishes of commercial and recreational fishing interest on the 

 (ireat Barrier Reef, Vol. 1. Great Barrier Reef Marine Park 

 Authority Research Publication 33, 106 p. 



