Coulson et al.: Biological features of Achoerodus gouldii 
65 
Table 1 
Estimates of the von Bertalanffy growth curve parameters L x , k, and t 0 (and their lower and upper 95% confidence limits [CLs J ) 
for western blue groper (Achoerodus gouldii) caught off southwestern Australia (A) for all fish, (B) for females and males whose 
sex was determined from gonadal characteristics, (C) for the same fish as in B but according to whether they were green or blue, 
and (D) for fish whose sex was determined by using either gonad type or the likelihood of the fish being female or male on the 
basis of a combination of its length and color. L x is the asymptotic length (mm), k is the growth coefficient (per year), t 0 is the 
hypothetical age (years) at which fish would have zero length, r 2 is the coefficient of determination, and n is the number of fish 
sampled. 
Category 
L x 
k 
*0 
r 2 
n 
A All fish 
Estimate 
111 
0.10 
-0.65 
0.84 
1855 
Lower, upper CL 
766, 789 
0.09, 0.11 
-0.90,-0.39 
B Females 
Estimate 
748 
0.12 
-0.15 
0.92 
854 
Lower, upper CL 
732, 764 
0.11, 0.12 
-0.30, 0.00 
Males 
Estimate 
975 
0.08 
-0.91 
0.35 
43 
Lower, upper CL 
879, 1072 
-0.02, 0.19 
-22.84,21.03 
C Green 
Estimate 
748 
0.12 
-0.17 
0.92 
836 
Lower, upper CL 
731, 765 
0.11, 0.12 
-0.32,-0.02 
Blue 
Estimate 
966 
0.08 
-0.10 
0.53 
61 
Lower, upper CL 
867, 1055 
0.03, 0.13 
-8.38, 8.18 
D Females 
Estimate 
682 
0.14 
0.06 
0.93 for both 
sexes combined 
1561 
Lower, upper CL 
675, 692 
0.14, 0.15 
0.00, 0.10 
Males 
Estimate 
982 
0.08 
-0.48 
132 
Lower, upper CL 
952,1013 
0.07, 0.09 
-1.09,-0.14 
its length and color (see Results). The resultant curves 
for the “females” and “males” fitted the length-at-age 
data very well (Fig. 4D), as is demonstrated by the high 
r 2 value of 0.93 for the model fitted to the data that pro- 
duced the two separate curves (Table 1). Although the 
L x estimated for the males shown in Fig. 4D was virtu- 
ally identical to that derived for males in the subset of 
fish sexed on the basis of their gonadal characteristics 
in Fig. 4B, the L x for females shown in Fig. 4D was less 
than that for females whose sex has been determined 
on the basis of their gonads, reflecting the presence of 
an increased number of older females and therefore an 
even greater tendency for the curve to reach an asymp- 
tote (Table 1). 
The relationship between total length (TL) in mm and 
total weight (W) in g for A. gouldii is InW = 3.041(lnTL) 
-11.017 (r 2 = 0.997, PcO.OOl, n=756) and the relation- 
ship between standard length (SL) in mm and total 
length (TL) in mm is TL = 1.201 (SL) - 11.883 (r 2 =0.995, 
Pc. 001, 72=101). 
Reproductive biology 
Temperatures in inshore and offshore waters at both 
Albany and Esperance underwent seasonal changes 
(Fig. 5, A and B). However, they were more pronounced, 
i.e., peaked earlier in mid-summer vs. early autumn, and 
reached their minima earlier, i.e., late-winter vs. mid 
spring, in inshore waters. Furthermore, the differences 
between water temperatures in inshore waters at the 
two locations in corresponding months were not as great 
as in offshore waters and, in some months, were greater 
at Esperance than at Albany. Although temperatures in 
deeper waters at Esperance on the south coast followed 
essentially the same seasonal trends as those at Albany, 
they were 1° to 1.5°C lower for each month. 
The mean monthly GSIs for female A. gouldii > the 
TL 50 at maturity, i.e., 653 mm (see later), remained 
low, i.e., <0.50 between December and May and then 
rose sharply to a peak of 2.3 in July, before declining 
to <1.6 in August to October and 0.1 in November (Fig. 
50. The gonads of all females collected between No- 
vember and May with lengths > the TL 50 at maturity 
possessed immature and resting ovaries (stage II). Fe- 
male fish with ovaries at stages III and IV were caught 
in June and July and those with ovarian stages V and 
VI, between June and October (Fig. 50. The above 
trends in the monthly female GSIs and the prevalence 
of females at different ovarian stages demonstrate 
that spawning occurs predominantly between June 
and October and that females with ovaries that de- 
velop beyond stage II will become mature during the 
spawning period. 
The smallest mature female (i.e., with ovaries at 
one of stages III — VII I ) caught during the spawning 
period measured 391 mm (Fig. 6A). The prevalence 
of mature females increased from 2% in the 350-399 
mm length class to >40% in all length classes above 
600 mm, and to 100% in fish >800 mm (Fig. 6A). The 
estimate for the TL 50 for female A. gouldii at matu- 
rity (and its 95% confidence intervals) was 653 mm 
(623-693 mm). 
