Hyndes etal.: Age composition, growth, reproductive biology, and recruitment of Sillaginodes punctata 
259 
of fish in those studies were determined by the 
growth zones on scales or whole otoliths, which in 
neither case had been validated as being formed an- 
nually (Scott, 1954; Gilmour, 1969; Caton 1 ; Jones et 
al. 3 ). The present study demonstrates that, in the case 
of the populations of S. punctata in southwestern Aus- 
tralian waters, the growth zones on scales are diffi- 
cult to discern and all of those on the otoliths of larger 
fish are only revealed after the otoliths have been 
sectioned. Data obtained from sectioned otoliths have 
thus been used to determine the age structure and 
growth rate of S. punctata on the lower west coast of 
Australia. Emphasis has then been placed on deter- 
mining the length and age at first maturity, the loca- 
tion and period of spawning, and the period during 
which S. punctata is recruited into its nearshore 
nursery grounds. The implications of these biologi- 
cal data for managing this important species are then 
considered. Our results have been compared with 
those obtained for populations of S. punctata else- 
where in Australia. We have also compared aspects 
of the biology of S. punctata with those of the five 
other whiting species in the same region, all of which 
belong to the genus Sillago and, in the case of S. 
schomburgkii and S. bassensis, are fished both 
recreationally and commercially. This comparison 
enabled us to elucidate the extent to which age com- 
position, growth, spawning period, and size-related 
shifts in habitat vary among the species comprising 
this abundant family. 
Materials and methods 
Small S. punctata, i.e. <300 mm, were collected from 
sites in nearshore marine waters (<1.5 m depth) be- 
tween latitudes 32°00'S and 32°31'S on the lower 
west coast of Australia between June 1991 and May 
1993 (see map in Hyndes et al., 1996a). Sampling 
was undertaken with a 21.5 m long seine net, which 
had a mesh size of 3 mm in the pocket. Large S. 
punctata, i.e. >300 mm, were obtained from recreational 
anglers, who were fishing between February 1993 and 
August 1996 in waters <50 m in depth between 31°55'S 
and 32°45'S. These anglers kindly supplied frozen car- 
casses, including gonads, after they had been filleted, 
together with a record of the date, location, and depth 
at which each fish had been captured. 
The total length (TL) of each fish was measured to 
the nearest 1 mm. When a gonad could be identified 
3 Jones, G. K„ D. A. Hall, K. L. Hill, and A. J. Stamford. 1990. 
The South Australian marine scalefish fishery stock assessment; 
economics; management. South Australian Department of 
Fisheries Green Paper, January 1990, 186 p. 
as either an ovary or a testis, it was assigned to one 
of eight developmental stages, according to the cri- 
teria of Laevastu (1965): I - virgin; II = maturing 
virgin; III - developing; IV = maturing; V = mature; 
VI - spawning; VII = spent; and VIII = recovering or 
spent. However, multiple spawning by representa- 
tives of this species in each spawning season (see 
“Results” section) meant that it was often difficult to 
ascertain whether certain gonads should be recorded 
as stages V, VI, or VII. The data for these three stages, 
subsequently referred to collectively as mature go- 
nads, were therefore pooled. It was not possible to 
recognize stage VIII gonads in males. Ovaries of the 
large female S. punctata collected in each month of 
the study were placed for 24 h in Bouin’s fixative 
and then dehydrated in a series of ethanols. The 
midregion of each of these ovaries was embedded in 
paraffin wax, cut transversely (6 pm) and stained with 
Mallory’s trichrome. The circumferences of 30 oocytes, 
where the section passed through the nucleus, were 
recorded to the nearest 5 pm by using the OPTIMAS 
(OPTIMAS Corp., 1994) computer imaging package. 
This enabled the diameters of these oocytes to be 
calculated. Because hydrated oocytes had collapsed 
as a result of freezing, their circumferences could not 
be measured. The oocyte measurements for fish in 
each calendar month during the three years of this 
study were pooled in order to provide histological data 
for up to 10 ovaries from each of those months. The 
terminology for the oocyte stages was adapted from 
that given in Khoo ( 1979). 
The length at which 50% of female S. punctata first 
attained maturity (L 50 ) was calculated by fitting a 
logistic function to the proportion of mature fish in 
each 50-mm length interval in the spawning period 
of June to September (see “Results” section) by a 
nonlinear technique (Saila et al., 1988) with a non- 
linear subroutine in SPSS (SPSS Inc., 1994). The lo- 
gistic equation is 
P L =[l + e (a+bL) ]~ 1 
where P L - the proportion of fish with mature go- 
nads at length interval L; and 
a and b = constants. 
The L 50 was then derived from the equation 
L 50 = —ab 
Preliminary examination of scales and sagittal 
otoliths collected from large S. punctata caught dur- 
ing the initial stages of the study showed that growth 
zones were often difficult to detect in scales, whereas 
at least some growth zones could be clearly discerned 
