Cappo et al. : Causes and consequences of a latitudinal cline in the demography Lutjanus johnu 
313 
Table 1 
Fitted parameter estimates for the von Bertalanffy growth models for males (M), females (F), and 
all John’s Snapper ( Lutjanus johnii) sampled from the Kimberley, north Queensland, and Cape York 
regions in Australia during the period of February 1989-April 2002 (see Fig. 3, for graphs of growth 
curves by sex and region). L^=mean fork length (mm) of fish of age t (years), L 0<) =asymptotic mean 
length (mm), t Q =the hypothetical age at which the mean length is zero, K is the growth coefficient at 
which approaches L^. Standard errors of fitted parameter estimates are reported in parentheses, 
and the coefficient of multiple determination (R 2 ) and sample size (n) are also given. 
Region 
n 
Loo 
K 
to 
R 2 
Kimberley (M) 
255 
677.1 (20.53) 
0.17 (0.02) 
-0.81 (0.33) 
0.76 
Kimberley (F) 
294 
739.6 (27.05) 
0.16 (0.02) 
-0.62(0.29) 
0.79 
North Queensland (M) 
80 
819.7 (25.27) 
0.18 (0.02) 
-0.32 (0.36) 
0.85 
North Queensland (F) 
74 
851.4 (37.37) 
0.21 (0.03) 
0.34 (0.29) 
0.83 
Kimberley 
568 
698.0 (14.48) 
0.18 (0.01) 
-0.51 (0.20) 
0.79 
North Queensland 
216 
843.5 (15.66) 
0.19 (0.01) 
0.02 (0.16) 
0.87 
Cape York 
63 
685.1 (50.04) 
0.18 (0.05) 
-0.82(0.80) 
0.74 
to plot the maximum weights of John’s Snapper and 
6 other large lutjanids with latitude. These other spe- 
cies were Mangrove Jack (Lutjanus argentimaculatus), 
Twospot Snapper (L. bohar), Malabar Snapper (L. mal- 
abaricus), Emperor Snapper (L. sebae), Chinaman Fish 
( Symphorus nema top horns), and Green Jobfish ( Aprion 
virescens ). 
Results 
Length and age distributions 
Samples from north Queensland had the smallest (55 
mm FL) and largest (990 mm FL) fish, a higher modal 
FL (401-500 mm ) than the samples from the Kim- 
berley and Cape York regions (301-400 mm FL), and 
a much higher proportion of very large John’s Snap- 
per than samples from the other 3 regions (Fig. 2). 
The overall proportion of samples that were older than 
8 years in the Kimberley region (11.6%) was small- 
er than the proportion of such samples in the north 
Queensland region (18.2%) but similar to the propor- 
tion in the Cape York region (11%). The modal age (4 
years) for fish from north Queensland was higher than 
the modal age of fish from Kimberley (3 years), and 
the 6-year age class was most prevalent in the sam- 
ples from Cape York. The oldest year classes were from 
north Queensland (28 year), Kimberley (23 year), and 
Cape York (18 year). 
Mortality 
The maximum observed age (£ max ) of 28.6 years (a 
male) was used to produce an estimate of Z=0.146 
year -1 with the Hoenig (1983) equation for the north 
Queensland region. Estimates of Z were not calculated 
for the other regions because of concerns that the £ max 
values might be skewed by a lack of older year classes 
that represented undersampling and not truncation of 
the true age distribution. 
Growth 
The von Bertalanffy growth curves fitted to length-at- 
age data revealed a relatively moderate growth trend 
(Fig. 3). This trend was reflected in estimates for the K 
curvature parameter, which ranged from 0.17 to 0.21 
year -1 (Table 1). Relatively rapid growth from 0.5 year 
to 5-7 years was followed by a slower phase after ap- 
proximately 7-10 years. Asymptotic growth began at 
approximately 18-20 years (Fig. 3). 
Females were estimated to grow to a larger aver- 
age asymptotic length (LJ) in the Kimberley and north 
Queensland regions (Fig. 3; Table 1). However, sex-spe- 
cific differences in growth curvature, K, were inconsis- 
tent between regions; a higher K value was evident for 
males than for females in the Kimberley region and 
a lower K value for males than for females in north 
Queensland (Table 2). The north Queensland was 
17.3% (145.5 mm FL) and 18.8% (158.4 mm FL) higher 
than the for samples from the Kimberley and Cape 
York regions (Table 1; Fig. 3). 
Apparent differences in growth trends between sexes 
and regions were observed to be statistically significant 
in both the likelihood ratio and ANCOVA tests (Table 
2). Significant differences between sex-specific curves 
were detected within each of the Kimberley and north 
Queensland regions (Table 2). The lack of significant 
interaction for sex x region indicates that the larger 
Loo for females than for males was consistent among 
regions. 
Likelihood ratio tests revealed significant differ- 
ences in growth curves between samples from the 
