Kntzer: Sex-specific growth and mortality, spawning season, and female maturation of Lut/anus carponotatus 



99 



80 

 70 

 60 

 50 H 

 40 

 30 H 

 20 

 10 

 



rzL 



estimate an early growth rate of 

 0.76 mm/d, assuming daily period- 

 icity of micro-increments (Fig. 3). 

 This rate of growth represents quite 

 rapid growth, given that fish are 

 adding 100 mm of length in around 

 4 months, increasing from approxi- 

 mately 20 to 120 mm FL (Fig. 3). The 

 x-intercept of the early growth curve 

 (=-17.98 d) was divided by 365 d/yr 

 to estimate a common t (=-0.049 yr) 

 for all VBGF models. 



Although size at age for both sexes 

 at both island groups was character- 

 ized by substantial individual vari- 

 ability, different growth trajectories 

 were evident for males and females 

 (Fig. 4, A and B). Estimates (Table 

 2) and 95% joint confidence regions 

 (Fig. 4C) for the VBGF parameters 

 indicated that the primary differ- 

 ences in these trajectories at each 

 island group lay in L M (which indi- 

 cated that males grow larger than females). In 

 contrast, the common range of K values spanned 

 by the sexes within each island group indicated 

 similar curvature (Table 2, Fig. 4C). However, use 

 of a common t restricts the range of possible fitted 

 lvalues (Kritzer et al., 2001). In addition to the 

 differences between the sexes, the data revealed a 

 general pattern of larger body sizes at the Lizard 

 Island group (Table 2, Fig. 4). 



Mortality estimates at the Palm Island group 

 were slightly higher when all age classes beyond 1 

 year were included compared with exclusion of age 

 classes with n < 5 (Fig. 5). These higher mortality 

 estimates contrast with Murphy's (1997) finding 

 that truncation of the age structure results in 

 higher least-squares estimates of Z. The differ- 

 ences between mortality rates estimated with 

 and without age classes with n < 5 were minor 

 for both males (ANCOVA: df=l, 20; F=0.009; 

 P=0.92) and females (ANCOVA: df=l, 23; F=1.35; 

 P=0.26). Therefore, for comparisons between the 

 sexes, the estimates that included all age classes 

 greater than 1 yr were used. In contrast to the sex- 

 specific growth differences, Z estimates of 0.26/yr 

 and 0.29/yr (Fig. 5) corresponding to annual survivorship 

 of 77% and 75% for females and males, respectively, at the 

 Palm Island group were similar between the sexes (ANCO- 

 VA: df=l, 27; F=0.505; P=0.483). Murphy's (1997) results 

 also suggested that least-squares mortality estimates are 

 likely to be around 30% less than the true mortality rate 

 when n = 200 and the true Z = 0.2/yr. Correcting these mor- 

 tality estimates based upon this potential bias results in Z 

 estimates up to 0.37/yr and 0.41/yr for females and males, 

 respectively, with corresponding annual survivorship of 

 69% and 66%-. However, the catch curve estimates (Fig. 

 5) corresponded well with estimates based upon Hoenig's 

 (1983) empirically derived relationship between Z and 



n 



In 



I 



I 



□ Stage I 

  Stage II 



□ Stage III 

 El Stage IV 



I 



  



Bfl 



51 



1 I i ' ' i ii, mi i m 



co ,, 3"ir>cor--ooa>o-<-<Mco-si-ir><or^coa>OT- 



t-t-t-t-^t-t-CM<M<MCMCN(>J(N(MCM<MCOCO 



Size class midpoint (mm FL) 



Figure 2 



Size-frequency distributions of female Palm Island group Lutjanus carponotatus at 

 each of the four stages of ovarian development. Stage descriptions are provided in 

 Table 1. 



20 40 60 80 100 120 140 160 



Number of increments (age in days) 



Figure 3 



Fork length at microincrement count for Lutjanus carponotatus lack- 

 ing the first annulus at the Palm (□; n =24 ) and Lizard (■; n=25) island 

 groups. Periodicity of increments is presumed to be daily. Data from 

 each island group are distinguished, but a pooled linear growth curve 

 is presented as separate growth curves did not differ (ANCOVA: df=l, 

 46;P=1.07;P=0.301). 



maximum age, t max (females: t max =18 yr, Z=0.23/yr; males: 

 U,=16yr;Z=0.26/yr). 



The observed female-to-male sex ratios of 1.3 and 1.1 

 were close to unity at the Palm and Lizard Island groups, 

 respectively ( Table 2 ). However, x 2 tests suggest this ratio 

 is statistically different from 1 at the Palm Island group 

 ( df= 1; ^ 2 =7.74; P=0.005 ) but not at the Lizard Island group 

 (df=l;/ 2 =0.031;P=0.86). 



Age and size at maturity 



Although there was some indication that Palm Island group 

 females mature at slightly younger ages and smaller sizes 



