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International Journal of Marine Science 2013, Vol.3, No.47, 402-407
http://ijms.sophiapublisher.com
405
Sex ratios for the 1997–1998 data fluctuated between
0.45 and 1 with a mean of 0.63 ± 0.04 (Figure 2). The
overall sex ratio during 1997–1998 was 0.62, which
was significantly different from the expected sex ratio
of 0.5 (
χ
2
= 82.8 and P-value
<
0.01). The female
sardines dominated during all the months except in
June 1997 and January 1998, in both months the sex
ratio did not significantly differ from 0.5 (P
>
0.05).
During 2004–2008 sampling period, the females
outnumbered the males in all the months and the sex
ratios fluctuated between 0.29 and 0.98 with a mean
of 0.68 ± 0.02 (Figure 2). The overall sex ratio during
2004–2008 was 0.64 which was significantly
different from the expected sex ratio of 0.5 (
χ
2
=
129.6 and P-value
<
0.01). The male sardines
outnumbered the females in January 2007 [sex ratio
significantly differed from the expected sex ratio of
0.5 (P
<
0.01)], October 2007, and August 2008 [sex
ratio did not significantly differ from expected sex
ratio of 0.5 (P
>
0.05)].
Figure 2 Monthly sex distribution data for the samples
collected in 1997–1998 (empty) and 2004–2008 (filled) for the
Omani Indian oil sardine (
S. longiceps
)
The sex ratio during 1997–1998 did not show a
pattern for sardines with lengths below 19 cm and it
increased afterwards and was explained by the power
function (sex ratio = 0.002
L
2.03
,
r
= 0.92). Similarly,
the sex ratio for the period 2004–2008 showed a
pattern starting from the same length interval and was
explained by the following relationship (sex ratio =
6.7×10
-6
L
6.84
,
r
= 0.96) (Figure 3).
In the 1997–1998 samples, the occurrence of mature
sardines (stage III and above) were higher than
immature sardines (stages I and II) in February 1997
(61%), August 1997 (85%), January 1998 (55%), and
February 1998 (97%). On the other hand, the mature
Figure 3 Relationship between the lower total length interval
(cm) and the sex ratio for the Omani Indian oil sardine (
S.
longiceps
) on (A) 2004–2008 and (B) 1997–1998
fish dominated in 2004–2008 samples except in May
2004 (23%), March 2007 (26%), and May 2007 (42%)
(Table 2). During the period 2004–2008, 62% of the
samples were with 80–100% mature sardines, while
only 15% of the samples showed the same results in
1997–1998. It is worth mentioning that spent sardines
started to appear in large numbers in the samples
starting from March 2005, this is almost exactly when
the immature sardines (stages I and II) started to
disappear from the samples (Table 3).
3 Discussion
The female Omani Indian oil sardines outnumbered the
male sardines almost during all the sampling months.
The mean sex ratio of two sets of data used in the
current study of 1997–1998 and 2004–2008 were 0.63
± 0.04 and 0.68 ± 0.02, respectively. This suggests that
the Omani Indian oil sardines are multiple spawners.
This result was supported by the multiple spawning
peaks observed during the months; October, June and
July, September, June, and January and September in
2004, 2005, 2006, 2007, and 2008, respectively. The
Omani sardines are also reported to spawn in March,
August, and February (Al-Jufaili, 2011) and April
(Siddeek et al., 1994).