Heupel et at: Demographic characteristics of exploited tropical lutjanids 
423 
Age-based catch curves (Rick- 
er, 1975) were used to estimate 
the instantaneous rate of total 
mortality ( Z ) for each species. 
The natural log-transformed 
number of fish in each age class 
was regressed against the cor- 
responding age on the descend- 
ing slope of the age-frequency 
distribution to provide an es- 
timate of total mortality, Z. 
Regressions were fitted from 
the first modal age class, pre- 
sumed to be the first age class 
fully selected by the sampling 
gear, through the oldest age 
class that was preceded by 
no more than two consecutive 
zero frequencies. An ANCOVA 
was used to determine whether 
there were differences in mor- 
tality among regions for L. car- 
ponotatus. Z also was estimated 
by using the Hoenig (1983) esti- 
mator for fish populations from 
log e Z= 1.46-1.01 log e t max , where 
t max was the maximum observed 
age in years. 
Sex ratios and size- and age- 
frequency distributions were ex- 
amined to describe sex-specific 
aspects of population structure. 
Departure from a 1:1 sex ratio 
was tested with a chi-squared 
test by using Yates’s correction 
for continuity (Zar, 1999). 
Results 
A total of 7307 individuals of 
the seven lutjanid species were 
sampled, of which L. carponota- 
tus was the most abundant. The 
modal length in the sampled 
distributions differed among 
species (Fig. 2) and was larg- 
est for S. nematophorus (400- 
449 mm FL) and A. virescens 
(450-499 and 600-649 mm FL) 
Figure 2 
Length-frequency distributions for seven lutjanid species on the Great Barrier 
Reef between 1995 and 2005 (note difference in y axes). 
and smallest for L. fulviflamma 
(260—279 mm FL). Symphorus nematophorus and A. 
virescens had the largest maximum fork lengths of 885 
mm and 810 mm FL, respectively. Of the seven species, 
the sampled length ranges of L. carponotatus, L. ful- 
viflamma, and L. adetii were most similar, with 72%, 
89%, and 81% coming from the size range of 200-300 
mm FL, respectively. 
Age-frequency distributions varied considerably among 
the five species for which age was estimated. The modal 
age in the catch was 2 years for A. virescens, 3 years 
for S. nematophorus, 7 years for L. carponotatus, 8 years 
for L. gibbus, and 10 years for L. fulviflamma (Fig. 3). 
The catch of the two largest species (S. nematophorus 
and A. virescens ) consisted predominately of younger 
age classes (<6 yr), whereas the catch of smaller species 
(L. carponotatus, L. gibbus, L. fulviflamma ) included a 
higher proportion of fish sampled from older age classes 
(>8 yr; Fig. 3). The maximum age in the catch also 
