Watanabe and Nakamura: Growth of Sardinops melanostictus 
903 
137.0 E 137.5 E 
34.0 N 
34.5 N 
18 
34.0 N 
137.0 E 137.5 E 
34.5 N 
34.0 N 
137.0 E 137.5 E 
16 > 
17 
. \ 
__ 
— 34.5 N 
18 • 
137.0 E 137.5 E 
18 
-f- 34.0 N 
Figure 3 
Sea surface temperature distribution off Atsumi Peninsula in April and 
May of 1990 and 1991. 
and 7 May were young, from 10 to 23 d. 
Except for one larva hatched on 31 March 
(not used for backcalculation), all larvae 
caught on 27 April and 7 May hatched in 
April 1990. In 1991, ages of sardine lar- 
vae were 19-30 d. Larvae caught on 15 
April were all hatched in March. Those 
caught on 23 April were composed of 
March- and April-hatched fish. All larvae 
caught on 5 and 14 May were hatched in 
April except one which was hatched on 24 
March (not used for backcalculation). 
Plots of TL (mm) on OR (pm) of all indi- 
viduals could be expressed in an allomet- 
ric formula (Fig. 7). Size at age of indi- 
vidual larva was backcalculated on the 
basis of allometric OR-TL relationship for 
each larva from first feeding to capture. 
The 1990 March-hatched cohort grew lin- 
early to 25 d when fish reached 20.5 mm 
TL (Fig. 8). Mean growth rate of the co- 
hort from 4 d (6.3 mm TL) to 25 d was 0.68 
mm/d. Growth in the April-hatched cohort 
in 1990 was linear to about 13 d (13.1 mm 
TL, 0.83 mm/d), then slowed down. In the 
1991 March- and April-hatched cohorts, 
growth was linear to 21 d (21.2 mm TL, 
0.85 mm/d), and 20 d (19.2 mm TL, 0.79 
mm/d), respectively, declining thereafter. 
Larval TL at which growth started to de- 
cline occurred at the approximate size 
when immigration into the coastal fishing 
grounds occurred in both months. 
Total lengths at 15 d in the 1990 March- 
and April-hatched cohorts were 14.2 ±1.2 
and 14.9 ±1.4 mm, respectively, whereas in 1991 the 
March-hatched cohort reached 16.3 ±1.5, and the 
April cohort 15.8 ±1.3 mm. Backcalculated TLs of 
March- and April-hatched cohorts were significantly 
smaller in 1990 than in corresponding hatching 
month in 1991 at 15, 20, and 25 d (Table 1 ). 
Discussion 
Larvae of S. melanostictus and E. japonieus have 
been reported to be transported from the offshore 
Kuroshio area to the coastal fishing grounds along 
the Pacific coast in central Japan by onshore intru- 
sions of Kuroshio waters (Tsuji, 1983; Muranaka, 
1984; Mitani, 1990). This is the case in the coastal 
fishing grounds off Atsumi Peninsula, because great 
densities of S. melanostictus eggs were detected in 
the offshore waters along the Kuroshio Current in 
1990 and 1991 (Ishida and Kikuchi, 1992; Zenitani 
et al., 1995; Watanabe et al., 1996). Onshore intru- 
sions of Kuroshio waters often develop when the 
Kuroshio meanders in the waters off central Japan 
(Kobayashi et al., 1986; Kasai, 1995). The available 
population size of S. melanostictus larvae in coastal 
fishing grounds off Atsumi Peninsula and adjacent 
waters is a positive function of the latitudinal dis- 
tance from Cape Omaezaki to the Kuroshio axis (Fig. 
1) (Kishida et al., 1994). This distance in April and 
May 1991 measured approximately 125 nautical 
miles (n mi) (Maritime Safety Agency, 1991), which 
was less than that in 1990 (200 n mi) (Maritime 
Safety Agency, 1990). Oceanic conditions were less 
favorable for onshore larval transport in 1991 than 
in 1990. As seen in Figure 3, SSTs in coastal waters 
were lower in 1991 than in 1990, a feature that was 
indicative of limited intrusion of the warm Kuroshio 
waters to the coastal area. Annual catch of sardine 
shirasu in 1991 in the waters off Atsumi Peninsula 
(including small catches in Ise Bay) decreased to 41% 
