378 



Fishery Bulletin 103(2) 



20 



15 



1995 



L=1 .05-4-1.39 



n=102 r 2 =0.87 



1996 



L=0.65A-0 .15 



n=93 r 2 =0.80 

 i i 



12 



16 



A (d) 



Figure 8 



Relationships between standard length 

 (L, mm) and otolith-estimated age (A, d) 

 of S. niphonius larvae collected during 

 the cruises in late May of 1995 and 1996 

 in the Sea of Hiuchi. 



10 



2 8 

 o 



S e 



to 



1 4 



i 2 







1995 1996 



Year 



Figure 9 



Mean (SE) young-of-the-year S. niphonius abun- 

 dance collected by the seine fishery in 1995 and 

 1996 in the Sea of Hiuchi. Asterisk indicates a 

 significant difference between the years (Mann- 

 Whitney I/- test, P<0.01). 



availability for S. niphonius larvae fluctuated depending 

 for the most part on seasonal change in abundance of 

 gizzard shad larvae that were dominant in the Sea of 

 Hiuchi. The difference in clupeid larval abundance in 

 late May between 1995 and 1996 may be explained by 

 between-year difference in gizzard shad spawning stock 

 biomass. The total catch of gizzard shad in the south- 

 ern Sea of Hiuchi (coastal waters of Ehime Prefecture) 

 in 1995 (372 t) was higher than that in 1996 (217 t: 

 Ehime Prefecture Agriculture, Forestry and Fisheries 

 Statistics Association, 1998). 



Implications for recruitment 



Variability in larval growth rate can influence survival 

 during the larval period by affecting the length of the 

 early life stages because total mortality is positively cor- 

 related with the length of these early life stages (Houde, 

 1987). Campana (1996) demonstrated a significant corre- 

 lation between growth to the end of the pelagic juvenile 

 stage (90 d) and the year-class strength of Atlantic cod 

 on the Georges Bank and suggested that the adult cohort 

 strength could be predicted from growth during early life 

 stages. In the present study, egg and larval S. niphopius 

 abundance during their peak-occurrence period did not 

 differ between 1995 and 1996, whereas YOY and 1-year- 

 old S. niphonius were more abundant in 1995. These 

 results indicate more successful recruitment and higher 

 larval growth rate in 1995 although there are no data 

 available for years other than 1995 and 1996. Larvae of 

 S. niphonius initiate feeding at 5.59 mm SL at 18.5°C 

 (Shoji et al., 2002). Given the mean larval growth rate 

 in 1995 (1.05 mm/d) and 1996 (0.88 mm/d), the critical 

 period (from first feeding to the onset of schooling at the 

 early juvenile stage, 19.6 mm SL; Masuda et al., 2003) 

 is estimated as 13.3 days in 1995 and 16.5 days in 1996. 

 For S. niphonius, even a slight increase in larval stage 



duration due to retarded growth can greatly reduce 

 larval survival because the larval daily mortality coeffi- 

 cient is expected to be extremely high (>0.6: Grimes and 

 Kingsford, 1996). The lower recruitment of S. niphonius 

 in 1996 may be partly explained by the prolonged larval 

 period (3.2 d) which could have led to lower survival 

 (1/6.82, assuming the daily mortality coefficient is 0.6) 

 during the larval period of that year. 



Acknowledgments 



We thank M. Fukuda, N. Suzuki, N. Kohno, and the crew 

 of RV Shirafuji of NRIFEIS and staff of Asagi-Suisan 

 Co. Ltd. for their assistance with field sampling. We also 

 thank T. Maehara and N. Murata, Ehime Prefecture 

 Chuyo Fisheries Experimental Station Toyo Branch, 

 and Y. Maki, Kawarazu Fisherman's Association, for 

 their help in collecting young-of-the-year Japanese Span- 

 ish mackerel and data on the catch of 1-year-old fish. 

 Two anonymous reviewers and M. Takahashi, National 

 Research Institute of Fisheries Science, provided valu- 

 able comments on the manuscript. 



Literature cited 



Campana, S. E. 



1996. Year-class strength and growth rate in young 

 Atlantic cod Gadus morhua. Mar. Ecol. Prog. Ser. 135: 

 21-26. 

 DeVries, D., C. Grimes, K. Lang, and B. White. 



1990. Age and growth of king and Spanish mackerel larvae 



and juveniles from the Gulf of Mexico and U.S. South 



Atlantic Bight. Environ. Biol. Fish. 29:135-143. 



Ehime Prefecture Agriculture and Forestry Statistics Association. 



1998. Agriculture, forestry and fisheries statistics of 



Ehime Prefecture, fiscal 1996, 278 p. Ehime Prefec- 



