Ferreira and Russ: Population structure of Plectropomus leopardus 



633 



GLOW YANKEE 



CLOSED 



GRUB HOPKJNSON 

 OPEN 



GLOW YANKEE 



CLOSED 



GRUB HOPKINSON 

 OPEN 



Figure 2 



(A) Mean fork length of leopard coralgrouper, 

 Plectropomus leopardus, for each reef, and stan- 

 dard error bars (years pooled). (B) Mean age of 

 leopard coralgrouper for each reef, and standard 

 error bars (years pooled). Sample sizes are pre- 

 sented in Table 1. 



more appropriate to describe the growth data over 

 the age range 2 to 10 years for all reefs with the excep- 

 tion of Yankee, for which an asymptotic model was 

 more appropriate. No significant differences were 

 observed between the linear regressions obtained for 

 each reef (P=0. 276), indicating that the mean size at 

 age (and therefore growth) did not vary significantly 

 between the four reefs. 



Analysis of the age and size distributions at 

 each reef 



Glow and Yankee, the two closed reefs, had very 

 strong modes in the year classes 6 and 7 (Fig. 4). In 

 separating age distribution by year (Fig. 5), it is clear 

 that these modes represented a strong year class that 

 comprised 6-year-olds in 1990 and 7-year-olds in 

 1991. This result rules out the possibility of selec- 

 tion towards one year class by fishing gear or bias in 

 age determination. This strong year class was not as 

 obvious on the unprotected reefs (Fig. 5). At 



Table 3 



Schnute's (1981) parameter "a" and r 2 values for nonlin- 

 ear and linear growth models for leopard coralgrouper, 

 Plectropomus leopardus, ages 2 to 10 years. 



Closed 



Open 



Glow Yankee Grub Hopkinson 



Nonlinear r 2 

 Linear r 2 



0.080 

 0.450 



0.445 



0.102 

 0.546 

 0.448 



0.004 -0.040 

 0.754 0.669 



0.754 0.666 



Hopkinson, year class 6 formed a small mode in 1990, 

 but the pattern was not consistent, because year class 

 7 was not strong in 1991. At Grub, younger ages were 

 proportionally more abundant; the mode was in the 

 3-year-old class for two consecutive years. 



The 6+ year-old age class of 1990 and the 7+ year- 

 old age class of 1991 settled onto the reefs at the 

 beginning of 1984. Because Glow and Yankee have 

 been closed to fishing since 1987 and age of recruit- 

 ment to the fishery is approximately 3 years of age 

 (Ferreira and Russ, 1994), the individuals settling 

 onto Glow and Yankee in 1984 were protected from fish- 

 ing for most of their lives. Modal progression was not 

 particularly evident in the size distributions (Fig. 6). 



Sex structure 



The distribution of developmental stages by size and 

 age (Fig. 7) indicated that sex change occurs over a 

 wide range of sizes and ages on the four reefs. The 

 frequencies of developmental stages observed for 

 each reef (Table 4) were compared by using chi- 

 square analysis. The frequencies were significantly 

 different between all reefs (P<0.05), with the excep- 

 tion of the frequencies observed for Yankee and 

 Hopkinson (P=0.246). For the calculation of sex ra- 

 tio, frequencies of young males were pooled with fre- 

 quencies of mature males, because individuals in both 

 categories were sexually potential males. The result- 

 ing sex ratios (Table 4) were not significantly differ- 

 ent among reefs (P=0.09). 



There were no significant differences between pro- 

 tected and unprotected reefs, but some differences 

 between reefs were detected. The mean size of ma- 

 ture females was not significantly different between 

 reefs (one-way ANOVA, P=0.10). The mean age of 

 mature females, however, was significantly different 

 between reefs (log (age), P=0.008); mature females 

 from Glow were significantly older than mature fe- 

 males from Grub (post hoc, P<0.05). Age and size of 



