Cappo et al.: Causes and consequences of a latitudinal cline in the demography Lut/anus johnii 
315 
Table 2 
Comparison of regional growth data for John’s Snapper (Lutjanus johnii) from our study of a 
latitudinal cline in the demography of this species in Australia. Likelihood ratio tests, each with 3 
degrees of freedom (df), were performed for coincidence of curves (Curves). Tests of the probability 
(P) of differences among slopes ( p) and intercepts (a) were made for sex and region with 2-way 
analysis of covariance (ANCOVA) of fork length (mm) against log e (age) for samples from the 
Kimberley and north Queensland regions (df numerator:df denominator=l:672). Tests of slopes 
and intercepts were made only for region for Cape York and Kimberley with 1-way ANCOVA 
(df=l:616) and for Cape York and north Queensland (df= 1:256). P=probability of null hypothesis 
being true. If the chi-squared goodness of fit statistic (x 2 ) is large, the null model is a poor fit to 
the curve. The F statistic is the ratio of between-group mean square values to the within-group 
mean square values for slopes and intercepts. 
Factor 
Parameter 
Test statistic 
P 
Excluding Cape York data 
Kimberley 
Sex 
Curves 
X 2 =14.42 
0.00 
North Queensland 
Sex 
Curves 
X : =8.70 
0.03 
Males 
Region 
Curves 
X 2 =80.68 
<0.00 
Females 
Region 
Curves 
X 2 =99.58 
<0.00 
Kimberley, north Queensland 
Sex 
P 
F=9.47 
0.00 
Kimberley, north Queensland 
Region 
P 
F=35.89 
<0.00 
Kimberley, north Queensland 
SexxRegion 
P 
F=1.07 
0.30 
Kimberley, north Queensland 
Sex 
a 
F=4.51 
0.03 
Kimberley, north Queensland 
Region 
a 
F=3.00 
0.08 
Kimberley, north Queensland 
SexxRegion 
a 
F=0.67 
0.41 
Including Cape York data: sexes pooled 
Cape York, Kimberley 
Region 
Curves 
X 2 =2.06 
0.56 
Cape York, Kimberley 
Region 
P 
F= 1.45 
0.23 
Cape York, Kimberley 
Region 
a 
F=1.95 
0.16 
Cape York, north Queensland 
Region 
Curves 
X : =83.44 
<0.00 
Cape York, north Queensland 
Region 
P 
F=19.43 
<0.00 
Cape York, north Queensland 
Region 
a 
F= 3.98 
0.05 
(Table 3). Departures from a linear relationship were 
evident for older fish (>10 years), where the rate of 
otolith weight accretion appeared to decline with age 
(Fig. 4). 
Tests that spanned the widest age range, for the 
north Queensland region, showed no significant effects 
of sex on accretion rate, but there were significant dif- 
ferences in the coincidence of curves, slopes, and inter- 
cepts for pairwise comparisons of age ranges common 
between north Queensland and other regions (Table 4). 
Evidence of a difference in otolith weight at age between 
results for Kimberley and Cape York fish was equivocal 
because the fitted curves were not coincident, but the 
slopes and intercepts were not significantly different 
(Table 4). Cape York and Kimberley curves were inter- 
mediate between those from the north Queensland and 
Arafura Sea regions, showing a cline for an increasing 
rate of accretion of otolith weight with age and distance 
from the equator by about 0.2 g per degree of latitude 
for the oldest fish. Visual comparison of the regional 
fits with data from the Arafura Sea region showed an 
approximate two-fold difference in otolith weight at age 
beyond 10 years for north Queensland fish (Fig. 5). 
Gonad weight at length and maturity 
Exponential models provided the best fits for gonad 
weight at length (Table 5; Fig. 4), but the lack of data 
on gonad weights elsewhere severely restricted the 
tests in pairwise comparisons. There were no signifi- 
cant effects of sex for samples from north Queensland 
(Table 6), a finding that is not coincident with the 
Kimberley and Cape York fits. The tests on slopes and 
intercepts, however, were not significant. 
For fish with gonads that weighed >20 g, maturity 
was evident from macroscopic classification (Fig. 4). 
Minimum lengths and ages for the females of these 
mature fish were 690 mm FL and 9.83 years for north 
Queensland, 549 mm FL and 7.75 years for Kimberley, 
and 640 mm FL and 6.3 years for Cape York. Mini- 
mum lengths and ages for males that had gonads that 
weighed >20 g were 590 mm FL and 6.16 years for 
north Queensland, 590 mm FL and 9.75 years for 
Kimberley, and 620 mm FL and 9.33 years for Cape 
York (Fig. 4). In contrast, the Arafura Sea fish ap- 
peared to develop earlier. Fish sampled in that region 
