174 
Fishery Bulletin 119(2-3) 
2—4 zones 
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Month 
Figure 3 
Mean monthly marginal increments of sectioned otoliths, 
with 2—4 opaque zones and with >5 opaque zones, from 
Indian halibut (Psettodes erumei) caught by commercial 
trawlers between February 2014 and December 2015 and 
during research surveys between August 2015 and Sep- 
tember 2017) off the Pilbara coast in northwestern Aus- 
tralia. Error bars indicate standard errors of the mean. 
Sample sizes are given above error bars. Black bars on the 
x-axis indicate summer and winter months, and open bars 
indicate autumn and spring months. 
the lengths of 201, 287, 314, and 318 mm TL, respectively, 
attained by males at the same ages. 
Reproductive biology 
Mean monthly temperatures in offshore waters, adjacent 
to the Pilbara coast, increased steadily from a minimum 
of 24.4°C in August (late winter) to a maximum of 30.0°C 
in March (mid-autumn) before declining to 25.6°C in June 
(early winter) (Fig. 6). Day length was shortest in June (early 
winter) and longest in December (early summer) (Fig. 6). 
The mean monthly GSI for female Indian halibut rose 
sharply from 0.6 in July to a well-defined maximum of 6.6 
in October. Although it declined to 4.0 and 4.7 in December 
and January, respectively, the mean monthly GSI for 
females remained at levels >4.0 until February, after 
which it declined precipitously to 1.2 in April and to a min- 
imum of 0.6 in June (Fig. 6). The mean monthly GSI for 
male Indian halibut followed the same trend. 
Commercial trawl 
Females n=198 
Males n=208 
‘IL. 
Research trawl 
Females n=63 
Males n=74 
a 
Number of fish 
100 150 200 250 300 350 400 450 500 
Total length (mm) 
Commercial trawl 
Females n=193 
Males n=208 
el 
Number of fish 
Research trawl 
Females n=63 
Males n=74 
Ss 
Age (years) 
Figure 4 
Length—frequency and age—frequency distributions for 
female (black bars) and male (gray bars) Indian halibut 
(Psettodes erumei) caught as bycatch by commercial trawl- 
ers between February 2014 and December 2015 and with an 
otter trawl during research surveys between August 2015 
and September 2017 in the Indian Ocean off the Pilbara 
coast in northwestern Australia. n=sample size. 
All female Indian halibut sampled from May through 
July possessed ovaries that were either immature or rest- 
ing (stage 2) or spent and recovering (stages 7 and 8). The 
frequency of females with ovaries at such stages declined 
in August, when those with mature or spawning ovaries 
(stages 5 and 6) were first present (Fig. 7). The vast 
majority of females sampled between September and 
February had ovaries in stages 5 and 6. Although ~45% of 
females in March also possessed ovaries in those stages, 
a similar proportion of females had ovaries in stages 7 
and 8. The frequency of females with such ovaries 
increased to ~92% in April (Fig. 7). The trends in the fre- 
quency of occurrence of male Indian halibut with testes 
at different stages of development followed closely that of 
the females, in that males with mature or spawning 
