Watanabe and Nakamura: Growth of Sardinops melanostictus 
905 
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10 - 
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March 29 
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10 
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April 1 1 
March 9 
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20 30 40 
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March 26 
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April 16 
| March 6 | 
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30 
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I March 31 
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10 20 30 40 
20 
10 
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March 31 1 B [March 13 | 
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April 15 
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20 - 
10 1 | April 5 
April 23 
March 22 
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W W . W I 
i i i i m i i l l i i i i M ' i i ' n i i i i i i i i n i i 
10 20 30 40 
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April 27 
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10 - 
0 - 
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10 20 
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May 7 
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May 14 
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Age in days 
Figure 6 
Frequency distribution of age of sardine larvae caught on different dates in 1990 (left) and 
1991 (right). Boxes show the earliest or latest hatch date of the group. 
Table 1 
Back-calculated TLs (in mm) of sardine larvae at ages 10, 15, 20, and 25 d after hatching. 
Hatching month 
10 
15 
20 
25 
Mean 
SD 
n 
Mean 
SD 
n 
Mean 
SD 
n 
Mean 
SD 
n 
1990 
March 
10.8** 
0.9 
69 
14.1** 
1.2 
68 
17.5** 
1.4 
65 
20.5** 
1.3 
35 
April 
11.5 
1.0 
69 
14.9** 
1.4 
39 
17.9* 
2.0 
14 
1991 
March 
12.3 
1.1 
62 
16.3 
1.5 
62 
20.4 
2.1 
61 
23.1 
2.6 
33 
April 
11.7 
0.9 
110 
15.8 
1.3 
110 
19.2 
1.7 
110 
21.6 
1.8 
74 
* Significantly smaller (P<0.01) than the same hatching month cohort in 1991. 
** Significantly smaller PcO.001) than the same hatching month cohort in 1991. 
(April-hatched cohort) were caught from late April 
to early May. This finding indicates that large num- 
bers of small larvae were carried to the coastal fish- 
ing grounds after April 16 in 1990. The SST distri- 
bution in 8-9 May indicated that there was a sub- 
stantial amount of intrusion of the offshore warm 
water after 23-25 April. Because the size of immi- 
gration to the fishing ground was smaller in this 
April-hatched cohort than in others, decline of growth 
in this cohort started earlier, at 13 d old (13.1 mm 
TL), compared with other cohorts from 20 to 21 d 
(19-20 mm TL) (Fig. 8). 
Larval TLs at 20 d were 20.4 ±2.1 and 19.2 ±1.7 mm, 
as March- and April-hatched cohorts in 1991, respec- 
tively, which were comparable to the sizes at 20 d 
(19.1 ±0.6-19.4 ±1.6 mm) of the January- to March- 
hatched cohorts of S. melanostictus in the waters off 
Miyazaki in 1991 (Watanabe and Kuroki, 1997). In 
our current study, however, TLs of the 1990 larvae 
at 20 d ranged from 17.5 to 17.9 mm, significantly 
