313 Abstraet.-The recent age valida­ Variability in the population structure tion of the tropical snappers L. adetii and L. quinquelineatus has facilitated the comparison of growth, mortality, of Lutjanus adetii (Castelnau, 1873) and age structures for both these spe­ cies at the spatial scale of individual and L. quinquelineatus (Bloch, 1790) reefs. The age structure ofboth species among reefs within the Great Barrier among reefs in the central Great ReefMarine Park was based on counts ofannuli from sectioned otoliths. There Barrier Reef, Australia* was significant variability in growth, mortality, and age structures. Signifi­ cant differences in mean length, age. Stephen J. Newman and weight (independent of the sex of Australian Institute of Marine Science. PM.B. NO.3 the fish) were observed for both species Townsville, M.e., Queensland. 4810. Australia among reefs. Peaks in abundance of year classes were variable from reefto and reef. Comparisons of the von Berta­ lanffy growth curves indicated that the Department of Marine Biology. James Cook University pattern of growth in individuals of L. Townsville, 48 J 1, Australia quinquelineatus was significantly dif­ Present address: Western Australia Marine Research Laboratories ferent among reefs, whereas the pat­ Fisheries Department of Western Australia, PO. Box 20 tern of growth in L. adetii was not. North Beach. 6020, Western Australia However. there were no significant dif­ ferences in the mean length ofthe early age classes of either species among David MeB. Williams reefs. The mortality rates and hence Australian Institute of Marine Science, PM.B. NO.3 survivorship of both L. adetii and L. quinquelineatus among reefs were Townsville, M.e., Queensland, 48 JO. Australia highly variable. It is hypothesized that the varying age structures and mortal­ Garry R. Russ ity rates ofboth ofthese species at the spatial scale of individual coral reefs Department of Marine Biology, James Cook University are determined by the nonequilibrial Townsville, 48 J I, Australia balance of variable recruitment inter­ acting with density-independent mor­ tality. Hence the effect ofgood recruit­ ment years may persist in the age structure of populations over time. Spatial comparisons of life history among individual reefs within a parameters ofspecies ofthe family single geographic area has notbeen Lutjanidae have been undertaken undertaken. only amongbroad geographic areas Comparisons ofthe age structure (e.g. Nelson and Manooch, 1982). of lutjanids among a number of Likewise, the majority oflife history studies ofspecies ofthe Lutjanidae have been based on widespread col­ • Contribution 757 of the Australian Insti­ lections of individuals from broad tute ofMarine Science. Townville. Queens­ geographic areas (e.g. Druzhinin land. Australia. and Filatova, 1980; Loubens, 1980; 1 Sanders, M. J., S. M. Kedidi. and M. R. Liu andYeh, 1991; Davis and West, Hegasy. 1984. Stock assessmentfor the 1992; Sanders et a1.1; Mees2) and bigeye snapper (Lutjanus lineolatus) not on an individual reef scale. On caught by trawl in the Gulfof Suez. Food andAgriculture Organization ofthe United the Great Barrier Reef in Austra­ Nations Project for the Development ofFish­ lia, the fishing industry and other eries in Areas of the Red Sea and Gulf of resource users <e.g. tourists, rec­ Aden, FAOIUNDP RAB/83/023/08, 40 p. 2 Mees. C. C. 1992. Seychelles demersal reationalists, etc.) are managed fishery: an analysis ofdata relating to four under a system which protects ma­ key demersal species. Technical Report rine areas ofwhich individual coral 019. Seychelles FishingAuthority, Victoria, reefs are the primary management Seychelles, 143 p. 3 3 Great Barrier Reef Marine Park Autho­ Manuscript accepted 28 September. 1995. unit. To date, a comparison of age rity. 1985. Zoning the central section. Fishery Bulletin 94:313-329 (1996). and growth parameters oflutjanids Townsville, Australia. 3i4 Fi~hf>ry RlJilptin 94(2). J996 reefs within a single geographic area of the Great cerning the ecology of these species in Australian Barrier Reef have been published for only two spe­ waters. cies: the damselfishes Pomacentrus moluccensis and The recent validation (Newman et aU) of age and P. wardi (Doherty and Fowler, 1994, a and b). A num­ growth for both L. adetii and L. quinquelineatus has ber ofstudies have compared the abundance and size facilitated the comparison of demographic param­ structure of the serranid Plectropomus leopardus eters ofboth these species at the spatial scale ofin­ between reefs open to fishing and those closed to fish­ dividual reefs. The aims ofthis study are to examine ing.4.5.6 More recently, Ferreira and Russ (1995) have spatial variability in growth, mortality. and age struc­ examined the size, age, and sex structure ofpopula­ tures of populations of L. adetii and L. quin­ tions ofP. leopardus on closed and open reefs in the quelineatus among reefs within the central Great central Great Barrier Reef region. Barrier Reef region (Fig. 1>. 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 Materials and methods (100S-24°S) and occur as far as 34°S (Kuiter, 1993). The habitats ofboth species vary, although they are Sampling procedures most commonly associated with hard bottom areas. In the central Great Barrier Reefregion, L. adetii is Specimens ofL. adetii (11.=355) andL. quinquelineatus common at depths greater than 30 m within the (n=573) were obtained between October 1991 and midshelfgroup ofreefs and is known to occur on the December 1993 from fish traps (O-trap design with outershelfat depths up to at least 99 m, whereas L. 40-mm galvanized hexagonal wire mesh [Newman, quinquelineatus is common in both shallow and deep 1995]) used during a research program investigat­ waters on both midshelf and outershelf reefs to a ing the distribution and abundance oflutjanids among depth of at least 128 m (Newman, 1995). Loubens reefs inthecentral GreatBarrierReefregion (Newman, (980) has demonstrated that both species are rela­ 1995; Newman and Williams, 1995). Samples ofboth tively long lived and slow growing in New Caledonia; species were obtained from four reefs (Rib [RI], John similar conclusions have been obtained from the cen­ Brewer lJBJ, Lodestone [LO], and Kelso [KL]J; addi­ tral Great Barrier Reef (Newman et a1. 7). tional samples ofL. quinquelineatus were obtained from Neither ofthese lutjanids forms a significant por­ two otherreefs lDavies [DV] andMyrmidon [MRlJ (Fig. tion of the commercial catch in the central Great 1). Individual L. adetii <17 cm fork length (FL) and L. Barrier Reef, and they form only a nominal contri­ qui11.quelineatus <10 cm FL were usually not vulner­ bution to the recreational catch in this region (Higgs, able to trap fishing and specimens in this size range 1993; Newman, 1995). However, in the southern were therefore not obtained for analysis. Great Barrier Reef, L. adetii contributes a signifi­ Individuals ofeach species were measured (FL and cant proportion to the commercial lutjanid catch standard length [SL]I and weighed (clean weight after (Newman, 1995) and may become ofincreasing sig­ removal ofthe gills and viscera), and sexes were deter­ nificance to the recreational line fishery in future mined by macroscopic examination ofthe gonads. The years.s Relatively little information is available con- sagittal otoliths ofindividuals were removed and sec­ tionedlaterallythrough thefocus with a BeuhlerIsomet low-speed jewelry saw, and ages were determined ac­ 7 4 Ayling, A. M., and A. L. Ayling. 1984. Distribution and abun­ cording to the methods described in Newman et al. dance of coral trout species IPlectropomus spp.1 in the Swain group of reefs. Capricorn section ofthe Great Barrier ReefMa­ rine Park. Unpubl. report. to the Great Barrier Reef Marine Analysis of data Park Authority (GBRMPA; Project 171 I. Australia. 5 Ayling, A. M., and A. L. Ayling. 1986. A biological survey of Because a previous study (Newman et aU) indicated selected reefs in the Capricornia section ofthe Great BarrierReef Marine Park. Unpubl. report to the Great Barrier ReefMarine significant differential growth between sexes in both ParkAuthority (GBRMPA; Project 243 and 269), Australia. species, two-way factorial analyses ofvariance were 6 Ayling, A. M., and B. P. Mapstone. 1991. Unpublished data used to compare the mean length (FL, mm), age collected for GBRMPA from a biological survey of reefs in the (years), and clean weight (g) of each species both Cairns section ofthe Great BarrierReefMarine Park. Unpubl. report to the Great Barrier Reef Marine Park Authority among reefs and between sexes (in order to prevent IGBRMPAI, Australia. 7 Newman. S. J., D. McB. Williams, and G. R. Russ. Age valida­ tion. growth, and mortality rates of the tropical snappers (Pi­ 8 Williams, D. McB., and G. R. Russ. 1994. Review ofdata on sces: Lutjanidae), Lutjanus adetii (Castelnau. 1873) and L. fishes of commercial and recreational fishing interest on the quinquelineatus (Bloch, 1790) from the central Great Barrier Great Barrier Reef, Vol. 1. Great Barrier Reef Marine Park Reef. Australia. Submitted to Mar. Freshwater Res. (19961. Authority Research Publication 33, 106 p. Newman et al.: Variability in the population structure of Lutjanus adetii and L. quinquelineatus 315 ............ '" " ". /-" , .~. f ". , "J .~ ., .~ \' John Brewer"~ ~,.~ " Lodestone" h • .. ~.i .w ~. "". Davies 'J • "I\. ci~'<'( ., 19·00'8