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
...... '" " ". /-" , .~. f ". , "J .~ ., .~ \' John Brewer"~ ~,.~ " Lodestone" h • .. . ~.i .w ~. "". Davies 'J • "I\. ci~'<'( ., 19·00'8 j .. ~"
10 2(l 3::' "Iknel~
Figure 1 The locations of the reefs sampled for Lutjanus adetii and L. quin quelineatus from October 1991 to December 1993 in the central region of the Great Barrier Reef, Australia.
confounding differences among reefs with differences t = age ofthe fish; and between sexes). Both reefs and sexes were treated to = theoretical origin ofthe growth curve. as fixed and orthogonal factors in the analysis. Mul tiple comparisons were performed with Tukey's hon Von Bertalanffy growth curves were compared by estly significant difference (HSD) test (a=0.05). using the likelihood-ratio test (Kimura, 1980), con The Kruskal-Wallis one-way analysis of variance sidered the most robust measure (Cerrato, 1990). A by ranks was used to test for differences in the age modified analysis of the residual sum of squares structures of each species among reefs
in each age class (Nt) was plotted against their cor described in Newman et al.,7 with males larger than responding age (fl, and Z was estimated from the females in species (Tables 1 and 2). descending slope, b. Estimates of the survival rate of both species on different reefs were then calcu Age structures lated from the Z that was derived from catch curves, because Z =-loge S (Ricker, 1975). Age structures of L. adetii differed significantly among reefs IKruskal-Wallis statistic: H=13.85, P Table 1 Analyses ofvariance comparing mean length, age, and weight among reefs and between sexes for Lutjanus adetii (significant P values are in bold type) and a posteriori multiple comparison ofmeans using Tukey (HSD) analysis (a=0.05; reefs are pl"esented in order of decreasing magnitude). MS =mean square. Source ofvariation df MS F P Dependent variable: fork length (mm) Reefs 3 3106.15 12.912 < 0.001 Sex 1 462.23 1.92 > 0.15 Reefs x Sex 3 54.45 0.23 > 0.85 Residual 321 240.56 Dependent variable: age (years) Reefs 3 128.85 8.57 < 0.001 Sex 1 43.67 2.90 > 0.05 Reefs x Sex 3 7.24 0.48 > 0.65 Residual 320 15.04 Dependent variable: clean weight 19) Reefs 3 31684.62 14.70 < 0.001 Sex 1 23013.95 10.68 < 0.01 Reefs x Sex 3 799.39 0.37 > 0.75 Residual 288 2154.85 Tukey HSD analysis among reefs Fork length: Kelso Lodestone Rib John Brewer Age: Kelso Rib Lodestone John Brewer Clean weight: Kelso Lodestone Rib John Brewer Tukey HSD analysis between sexes Clean weight: Males Females Newman er al.: Variability in rhe popularion srrucrure of Lutjanus adetii and L. quinquelineatus 317 ferent from thatofLO. JB and LO had strong modes in Age structures ofL. quinquelineatus also differed yearclass 7, whereas KL suggested a mode inyearclass significantly among reefs (Kruskal-Wallis statistic: 9 (Fig. 2), The abundance ofyear classes 10-22 at LO H=21.41, p 22 Rib 20 :..':'lo.,. IS .. ,. n - 121 16 .~; ~.:: ".. 14 . " ":." ::~~:- 12 ,. 10 • l:' 8 :..:", .", b 4 0 0 4 8 10 I 14 I" IS 20 22 24 2S JlIhn On'wel' n = 84 20 I, ," IS ~S ... ~ t: '0: 10 .~.'. .:-: ...>. 5 0 & 0 18 20 22 24 J: 2S LlIdestllll~ n - 126 20 IS 10 Ih 1M 20 22 24 Kelsll n - 23 ..•.... ;:";. f" ~:~: Age (years) Figure 2 Age-frequency distributions for L. adefii among reefs in the central Great Barrier Reef. ,.n ~IO Fishery Bulletin 94(2), J996 Table 2 Analyses of variance comparing mean length, age, and weight among reefs and between sexes for Lutjanus quinqueLineatus (significant P values are in bold type) and a posteriori multiple comparison ofmeans using Thkey (HSDl analysis (u=0.05; reefs are presented in descending order). MS = mean square. Source of variation df MS F P Dependent variable: fork length (mml Reefs 5 5944.89 25.70 < 0.001 Sex 1 19962.29 86.31 < 0.001 Reefs.< Sex 5 166.94 0.72 > 0.60 Residual 551 231.29 Dependent variable: age (years) Reefs 5 547.00 17.03 < 0.001 Sex 1 40.95 1.27 > 0.25 Reefs>. Sex 5 41.13 1.28 > 0.25 Residual 550 32.11 Dependent variable: clean weight (g) Reefs 5 28723.22 35.83 < 0.001 Sex 1 98157.42 122.45 < 0.001 Reefs Thkey HSD analysis among reefs Fork length: Kelso Davies Rib John Brewer Myrmidon Lodestone Age: Kelso Rib John Brewel' Davies Myrmidon Lodestone Clean weight: Kelso Davies Rib John Brewer Myrmidon Lodestone Thkey HSD analysis between sexes Fork length: Males Females Clean weight: Males Females entfrom all other reefs. KL was not significantly dif Table 3 ferent from RI, but was significantly different from Differences in the distribution ofage structures ofLutjanus all other reefs. JB was not significantly different from adetii between reefs were determined by using the either DV or RI, whereas DV was significantly dif Kolmogorov-Smirnov test (values ofDmax are shown, sig nificance level a=0.05, significant results are marked with ferent from RI. MR showed a peak in year class 5 an asterisk [*]l. and relatively strongyear classes 6, 7, and 8 (Fig. 3). However, few fish older than 8 years were repre Reef sented in catches. LO had relatively strong year classes 2, 3, 4, and 5, but abundance per age class Reef John Brewer Lodestone Kelso declined rapidly to year 26, except for a strong mode Rib 0.38* 0.17 0.19 in year class 14 Table 4 Differences in the distribution of age structures of Lutjanus quinquelineatus between reefs were determined by using the Kolmogorov-Smirnov test (values ofDmox. are shown. significance level a=0.05, significant results are marked with an asterisk [*]l. Reef John Brewer Lodestone Davies Myrmidon Kelso Rib 0.14 0.31* 0.23* 0.43* 0.14 John Brewer 0.27* 0.20 0.43* 0.27* Lodestone 0.35* 0.30* 0.41* Davies 0.28* 0.36* Myrmidon 0.54* i.e. Myrmidon Lodestone Davies John Brewer Rib Kelso other reefs, older year classes were relatively domi The von Bertalanffy model provided a better de nant at KL. JB and RI had relatively flat age distri scription ofthe length-age relationship among reefs butions for year classes 2-24 compared with those for L. quinquelineatus (Fig. 51, with coefficients of for LO, DV, and MR. The only pattern that was con determination among reefs ranging from 0.267 to sistent across all reefs was the strong mode of5-year 0.752. The younger and smaller fish were under old individuals (Fig. 3), and this may have reflected represented in the catch samples from some reefs the age at which these fish attained full recruitment and this was reflected in the coefficients ofdetermi to the sampling gear (fish traps). nation (Table 5; Fig. 5). The parameters of the von Bertalanffy models for L. quinquelineatus among Growth models individual reefs were characterized by relatively small asymptotic standarderrors (Table 5). The growth The von Bertalanffy models of the length-age rela curves for L. quinquelineatus were significantly differ tionship among reefs for L. adetii are shown in Fig ent among reefs (likelihood-ratio test, P 10,------·------, 13,------, 9 Rib 12 D.wl"s n - 109 II I' IlJ II = 63 7 9 •7 b S 4 3 1 oL--J..""-...... J...I,;...... """'.:I-L"'-....L:.I.....L:.I.__..,-_--' II 2 4 6 II HI 12 14 Ib III 211 22 24 21> 21' 30 32 14 211 John B.'\'w"r Mynllicion 12 I. n = 108 II = 75 Ib IlJ f·' 14 >. I' 12 ~. ,. l:!QJ ::s 0" b 12 I~ ~d~ u.. . I ()~ .;·L~.L~Lt,1,;tb-Fl"":": J L-_J,,;r::..J.,l(iL.' :¥ ....Ln....L. . II D. II 2 4 6 • IlJ 12 14 16 II' 20 22 24 2b 21' 311 32 II 2 4 6 • 10 12 14 16 I. 211 22 24 26 2. 311 32 24,------, 22 ;. Lodestone Kelso 211 ":~? : 11- 175 n -42 II' Ib 14 2 '.. '" ~. I. 20 22 24 2b 21' 311 32 II 2 4 6 • IlJ 12 14 16 I. 211 22 24 26 2. 311 32 Age (years) Figure 3 Age-frequency distributions for L. quinquelineatus among reefs in the central Great Barrier Reef. Newman et al.: Variability in the population structure of Lutjanus adetii and L. quinquelineatus 321 parison ofslopes indicated that the mortality rate at derived from catch curves. Estimates of mortality Rib Reefwas significantlylower than thatat all other with high coefficients ofdetermination were obtain reefs (RI<[JB=LO=KL]). able from only two reefs, LO and MR. The other reefs. Individual L. quinquelineatus <5 years ofage were had a poor fit to the catch-curve regressions (Fig. 7), usually not fully recruited in the sampled popula and hence mortality rates were not obtained either tion and were excluded from the mortality estimates because there was a persistence ofnumerous strong 2XO o o • 240 : 0 .0i 0.' .. . o o I-- III' 0 0 200 o 00 0 Rib 11,0 L, = 290.8 (l_e-0.0399 (I + 34.09») 120 r 2 - 0.257 I XO I 40 '----_~~_,J 0 0 x 10 12 14 II' IX 20 22 24 o 2XO --tr-----.-----'~I 240 o 0_.:Jl-i-l.:-{-'a-;.0 o 0 200 John Brewer I(JO L, - 266.7 l1_e-0.0769 (I + 20.061) I 120 ,.... e Xli ~ e 40 '-" '---- ..:J .c 1i1 0 C 0 X 10 12 14 II' IX 211 22 24 u ...l ~... 2XII I 0 r.... 240 •: •• I 2011 Lodestone 160 L,- 270.4 (I_e-0.1336(,+ 8.613») 120 r2 - 0.462 XO 411 0 0 I' X 10 12 14 16 IX 211 22 24 2XO 0 . . •I o o 240f,---- . :. 2110 Kels.. L, = 296.8 ( l_e-O.0466 (' + 32.22) 120 r2 - 0.333 XO 40 0'------' o 2 4 x 10 12 14 16 IX 20 22 24 Age (years) Figure 4 Von Bertalanffy growth curves and observed length at age for L. adetii among individual reefs in the central Great Barrier Reef...... JLL Fishery Bulletin 94(2). J996 Table 5 Growth parameters and asymptotic standard errors (ASE) calculated from the von Bertalanffy growth function, mean fork length (FL, mm), and age (years) for Lutjanus adetii and L. quinquelineatus among reefs in the central Great Barrier Reef(GBR). LutjanU8 adetii Reefs All reefs pooled Rib John Brewer Lodestone Kelso central GBR Parameters (n=122) In=84l (n=126) (n=23l (n=369) L~(FL) 290.8 266.7 270.4 296.8 265.2 ASE 59.95 34.27 8.93 119.4 4.229 K 0.0399 0.0769 0.1336 0.0466 0.1454 ASE 0.0511 0.0959 0.0484 0.1638 0.0285 to -34.09 -20.06 -8.613 -32.22 -8.077 ASE 31.26 22.10 3.961 94.31 2.132 r2 0.257 0.177 0.462 0.333 0.390 FLmrnn (SEI 240.3 (1.48) 234.6 (1.67) 242.0 (1.391 256.7 (2.59) 241.1 <0.88) FLmin 185 196 209 233 185 FLmax 285 301 291 291 301 t",rnn (SEI 10.24 <0.397) 7.79 (0.350> 8.93 10.314) 11.17 (0.9341 9.27 <0.206) tmin 2 3 3 7 2 tmax 24 23 21 22 24 Lutjanu8 quinquelineatu8 Reefs All reefs pooled Rib John Brewer Lodestone Davies Myrmidon Kelso central GBR Parameters (n=110) In=108) (n=175) (n=63) (n=75) (n=42) (n=577l L~(FL) 214.1 204.1 198.1 211.5 208.0 220.4 206.9 ASE 5.221 1.665 1.697 2.417 11.26 2.72 0.979 K 0.1125 0.3138 0.4665 0.3048 0.1711 0.2182 0.3064 ASE 0.0433 0.0506 0.0367 0.0694 0.1290 0.0474 0.0174 to -14.12 -2.789 -1.108 -2.313 -8.238 -3.978 -2.587 ASE 5.774 0.8787 0.1942 1.456 7.443 1.588 0.2708 r-. 0.421 0.652 0.745 0.603 0.267 0.752 0.638 FLmrnn (SE) 198.5(1.5) 193.2 (1.5) 180.311.9) 199.3 (1.6) 190.5 (1.3) 207.0 (2.81 191.6 (0.8) FLmin 148 146 60 163 170 155 60 FLmax 231 230 230 224 219 233 233 t mean (SE) 11.6 <0.66) 10.2 <0.59) 6.9 <0.391 9.06 (0.601 6.65 <0.28) 13.43 (1.21) 9.12 <0.251 tmin 2 2 <1 3 3 2 <1 tmax 31 25 25 22 16 30 31 year classes or because there were age-varying mor total rate of mortality, Z, of L. quinquelineatus at tality rates (Fig. 7). The estimates oftotal mortality LO in 1992 was 0.176 (fish aged 4-17 years, r 2=0.615, rate, Z, ofL. quinquelineatus atLO and MR were 0.153 SE=0.0402, n=109), representing an annual survi (fish aged 4-22 years, ,.2=0.711, SE=0.0245) and 0.335 vorship of approximately 84% (Fig. 8), whereas the (fish aged 5-16years, ,.2=0.661, SE=0.0703), represent total rate of mortality, Z, of L. quinquelineatus at ing an annual survivorship ofapproximately 86% and LO in 1993 was 0.155 (fish aged 3-14years, ,.2=0.409, 72%, respectively. Mortality rates ofL. quinquelineatus SE=0.0621, n=64), representing an annual survivor between LO and MR reefs were significantly different ship of approximately 86% (Fig. 8). The mortality (homogeneity of slopes test, P Table 6 Mean length (FL. mml ofearly age classes ofLutjanus adetii among reefs and analyses of variance comparing the mean lengths ofindividual age classes among reefs. Number ofsamples per age class is in parentheses. ns = not significant. Reefs Rib John Brewer Lodestone Age class MeanFL MeanFL Mean FL df F p 2+ 199.0 (l) - (0) - (0) 3+ 196.0 (2) 226.5 (2) 209.0 ll) 4+ 203.0 (1) 238.3 (4) 226.0 (3) 5+ 227.0 III 212.2 (5) 226.3 (7) 6+ 237.1 (71 228.5 (17) 234.1 (17) 2,38 0.744 ns 7+ 231.3 (20) 233.21261 234.4 (27) 2,70 0.507 ns 8+ 235.3 (22) 239.6 Ill) 238.9 (21) 2,51 0.920 ns 9+ 238.3 (21) 245.5 (6) 243.9 (9) 2,33 1.825 ns Table 7 Mean length (FL, mm) of early age classes of Lutjanus quinquelineatus among reefs and analyses of variance comparing the mean lengths ofindividual age classes among reefs. Number of samples per age class is in parentheses. ns =not significant. Reefs Rib John Brewer Lodestone Davies Myrmidon Kelso Age class MeanFL Mean FL Mean FL Mean FL MeanFL Mean FL df F P 1+ 113.0 (8) 2+ 163.0 (3) 160.5161 154.3 (20) 155.0 (1) 3,26 0.523 ns 3+ 179.9 (7) 167.6 (7) 166.8 (22) 163.0 C1l 174.0 ll) 172.0 (2) 5,34 1.171 ns 4+ 185.0 (8) 179.1(8) 179.1 (23) 180.0 (3) 181.1 (8) 173.0 (1) 5,45 0.360 ns 5+ 188.7 (91 187.2 (13) 186.8 (20) 191.7 (10) 187.8 (201 193.6 (5) 5,71 0.984 ns 6+ 193.4 (7) 195.7 (3) 188.6 (14) 193.4 (12) 189.4 (13) 193.0 (2) 5,45 0.754 ns Discussion mean lengths ofindividuals in age classes 2-6 among reefs (Table 61. These results indicate thatinitial growth The significant differential growth in length and rates among reefs were not significantly different and weight ofboth species among reefs and between sexes that the significant differences in the overall growth indicates that rates of growth in terms ofweight at rates among reefs probably reflected the number of length of both species was variable at the spatial young fish available for capture at each reef. scale of individual reefs. However, statistical and The necessary pooling ofsize-at-age data over two visual comparisons ofthe VBGF for L. adetii indicate differentyears may have biased the resultinggrowth that the pattern ofgrowth in individuals among reefs patterns, ifgrowth was variable among years. There withincreasingage wasrelatively similar. Because only was, however, no evidence to suggest that growth of one gear type was used and the distribution ofjuvenile either species was variable among years. The pool L. adetii was not determined and is presently not ing ofdata over a number ofyears was necessary in known, it was not possible to obtain a sufficient range order to sample a wide cross section of age classes. of sizes to describe the first few years of growth. The The inclusion of size-at-age data over a number of growth patternsofL. quinquelineatus described by the years has the advantage of providing a general de VBGF were significantly different among reefs. How scription of the growth patterns of each species at ever, no significant differences were detected in the each reef. However, large sample sizes covering a JL"T". Fishery Bulletin 94(2), J996 range of age classes from a number of consecutive mented in the commercial catches ofmany temperate years would be needed to determine ifgrowth rates species (Hjort, 1914; Sissenwine, 1984; Rothschild, were variable between years. 1986> and has recently been observed in a number of The age structures for populations ofL. adetii and tropical species 240 2411 ••• •••:•: l-:';~--- •• • .:_....c.....::.:.-- _ 21111 ·Il""'ll"'~·if"-T.;'. 21111 I·tH,.-L-.---:-;-. • ...... •,. .: .. •••• • I .' .. Davies 160 •• 160 .... • Rib L, - 211.5 (I-e-0.3048 (' + 2.313» 1211 12111/ L,. 214.1 (I_e-o·1125 (1+ 14.12» ,.2- 0.603 "II ,.2 - 0.421 KO 411 411 oL- ---.J IIL------.J II 4 6 " III 12 14 16 I" 20 22 24 21> 2" 311 32 II 2 4 6 " 10 12 14 16 I" 211 22 24 26 2" 311 32 240 240 •• ••• -.~---.------200 ., II· ·.--.. 2011 ,.ii '·1 !-Hlt: I·::i.: ," ...... '-I·' '. .• ~ B~er 160 1611 .. ! John Myl'mldon O3138 120 ,/ L,· 204.1 (l_e- . (. + 2.1891) 1211 L,- 208.0 (I_e-O.1111 (' + 8.238) ,.2 - 0.652 2 "II "II r - 0.267 40 40 oL- ---.J IIL------.J II 2 4 6 " III 12 14 \6 I" 211 22 24 26 2" 30 32 II 2 4 6 " 10 12 14 16 IK 20 22 24 26 2" 311 32 240 2411 • • ." ,-'--"-1---.--,---=---""'-..- .... 200 .1·tett+e'I·.:· .: •• • 2UO ...... ,...... , . t '1." • I :' • Kelso 1611 f·• .' 1601/~ ,. Lodeltone L,- 220.4 (I_e-O.2182 (, + 3.978» 120 I L, - 198.1 (I_e-0.4645 (, + 1.108» 120 2 "II r - 0.745 "0 ,'-Q'" J 411 40 oL------' II II 4 6 " 10 12 14 16 1K 20 22 24 26 2" 30 32 II 2 4 ti " III 12 14 16 I" 20 22 24 26 2" 30 32 Age (years) Figure 5 Von Bertalanffy growth curves and observed length at age for L. quinquelineatus among individual reefs in the central Great Barrier Reef. Newman et al.: Variability in the population structure of Lutjanus adetii and L. quinquelineatus 325 Doherty and Fowler, 1994b)' Further. the suggestion Ricker, 1975; Gulland, 1983; and Russ, 1991). The that recruitment variability is a major factor influenc mortality rate for L. adetii was significantly differ ing both the distribution and local densities of coral ent among reefs, although these differences were reef fishes has been recognized for a number ofyears small. The mortality rates for this species in general (Williams, 1980; Doherty. 1981. 1983, 1991; Victor, 1983; were low and the rates of survivorship were corre reviews ofDoherty andWilliams, 1988). Subsequently. spondingly high. Mortality rates for L. quinque Doherty and Fowler (1994b) have shown that for the lineatus were not obtainable from all reefs owing to common tropical damselfishPomacentrus moluccensis. either the persistence of strong year-class modes, age structures from individual reefs have preserved ma (possibly to nonconstant mortality rates at a num jortemporal variations in the recruitment patterns over ber ofreefs (although these were not detected among at least 10 years, providing empirical evidence of a years at Lodestone Reef), or differential mortality of strongeffectofrecruitmenthistory on subsequentyear cohorts (as opposed to interannual variability in class strength. Itis therefore conceivable thatthe vari mean [cross-cohort] mortality rates). The results ob ous age structures ofboth lutjanid species among reefs served here suggest that interannual variation in is a consequence both of variability in recruitment at recruitment may be retained in the age structure at the localized scale of individual reefs and of good re each reef as found for P. moluccensis (Doherty and cruitmentyears persistingin the age structure ofpopu Fowler. 1994b). Mortality rates derived with the lations over time. catch-curve method ofBeverton and Holt (1957"1 and Estimates of the rate of natural mortality in fish Ricker (1975) are based on the assumption that re populations are essential to fishery management (see cruitment is constant in the population under con- Table 8 Analyses of covariance comparing weight at length (transformed to log•• covariate =length) among reefs and between sexes for Lutjanus adetii and L. quinquelineatus (significant P values are in bold type; note Kelso Reef was not included in the analyses because ofthe small sample size) and a posteriori multiple comparison of means using Thkey IHSDI analysis (a=0.05 ,. Source ofvariation df MS F P L.adetii Reefs 2 0.0328 11.917 < 0.001 Sex 1 0.0484 17.577 < 0.001 Reefs x Sex 2 0.0004 0.127 > 0.85 Residual 266 0.0028 Thkey HSD analysis among reefs Lodestone Rib John Brewer Thkey HSD analysis between sexes Males Females L. quinquelineatu8 Reefs 4 0.0683 15.647 < 0.001 Sex 1 0.0258 5.907 <0.05 Reefs x Sex 4 0.0129 2.948 <0.05 Residual 510 0.0044 Thkey HSD analysis among reefs Male: Rib Davies John Brewer Myrmidon Lodestone Female: Rib Davies John Brewer Myrmidon Lodestone Thkey HSD analysis between sexes Rib: Males Females John Brewer: Males Females Lodestone: Males Females Davies: Males Females Myrmidon: Males Females 326 Fishery Bulletin 94(2). J996 sideration. Mortality estimates derived with the total mortality and high rates ofsurvivorship. How catch-curve regression method are least sensitive to ever, mortality estimates cannot be derived with minor violations of this assumption (Ricker, 1975) great confidence from populations where significant and this is particularly evident in L. quinquelineatus. recruitment variability is retained in the age struc Despite this, it is evident from Figure 7 that mortal ture (e.g. Ferreira and Russ, 1995), and although ity rates of L. quinquelineatus are variable among Ricker (1975) has suggested that irregularities in reefs and are similar to those for populations of L. catch curves caused by variable recruitment can be adetii in that they are characterized by low rates of reduced by combining samples over successive years, .15,------.c------~.~ ••• ." - 3.999 - 0.179x 2 25 r - 0.729 I loges 8-24 yea~ only) u •• •I 11.5 U ----_._--_.~-~- II 12 1(, 20 24 '15 -'-'. John B....wer .' • ." - 4.484 - 0.304 .t 2.5 r'·0.512 (oges 7-15 yeors only) 21 r:~L_~~~' .~_.J C1' U 4 K 12 ..'II, 20 24 ~ .1.5,------'" ..5 .-Lodestune I ." = 4.44.' - 0.225 x I 2.5 r' =0.781 .'.~.,." ~~J u · 1l.5 U II K 12 HI 211 24 2 .------'--.------K-.e-.Is-o---I ." - 3.979 - 0.286 x /.2 = 0.795 (ages 9-15 years onlyI I 1l.K I I U-:I__..__._ • . 1 II 4 12 II> 2U 24 Age (years) Figure 6 Catch curves for L. adetii among reefs, based on observed ages. Newman et al.: Variability in the population structure of Luljanus adetii and L. quinquelineatus 327 2.4 Rib DlIvles 2.4 • •• • 2 •• • • y-2.141-0.0916x ••• • r 2 = 0.332 16 •• I.K • • • (ages 6-22 years only) \.2 •• ••• ••• 12 • •• O.K • 0.6 ••• •• 0.4 0 0 0 5 \II 15 20 25 30 II 5 \II 15 20 25 311 3.2,-----.,-\------. John BI'flYrl' \• Myrmidon y - 2.201 - 0.0I.i49.f 2.41 . ... ·· 2.4 \ .. y - 4.048 - 0.284 .t r 2 = 0.312 2 IK • r - 0.672 (ages 5-24 years only) .\'\\ (ages 5-16 years only) 0... • . 16 12L··· O.K I 0.6 ••• • .E \. '. '. oL-~ ~_ ___>.~ ___l I) -----~------' o 5 \II 15 2S 30 II 5 \II 15 20 25 30 3.5 Lodestun.. K..INo 3 ••... 16 •• • y - 3.408 - 0.153x I 2.5 ' .. ~ • = 0.711 12 ". • 2 ... • (ages 4-22 years only) I.S • O.K • •••• •• •• •• I • •• 0.4 0.5 ••• 0 0 0 5 III IS 20 25 30 I) 5 \II 15 20 25 31) Age (years) Figure 7 Catch curves, based on observed ages. for L. quinquelineatus among reefs. this method was not expected to reduce variability relatively consistent through time. Similarly, Doherty among age classes in the present study. and Fowler (1994a) suggested that mortality sched However, the mortality rates ofL. quinquelineatus ules were consistent (not constant) across space and at Lodestone Reef were not significantly different time for two damselfish species from the positive cor between successive years (Fig. 8). This result sug relations that were present between spatial and tem gests that the variable mortality rates and hence poral variation in recruitment and subsequent abun survivorship of these species among reefs may be dance. Therefore, the observed differences in mor- 3llj Fishery Bulletin 94(2). 1996 3 o = 1992 o 0 Lodestone ( 1<)92) • • = 1993 /Ii'. Z = 0.176 II"> = 0.615) 2.4 o (ages 4-17 only) >. 0 0 .....•. ~ 0 o ~ 1.8 C" °A:"'~O ~ : 0'·...... E 1.2 0 • • Lodestone (19<)3) • 0 .... o 0.6 Z = 0.155 II"' = 0.409) (ages 3-14 only) oL-.. ~~~_~~_"'_~...."...~_<>_...... >__~_.J o 2 4 6 8 10 12 14 10 18 20 22 24 26 Age (years) Figure 8 Catch curves for L. quinquelineatus from Lodestone Reef between suc cessive years, based on observed ages. tality rates among reefs for these species are likely Acknowledgments to be authentic and not a product ofthe assumptions inherent in the use ofcatch curves. This work was undertaken while S. J. 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