202 



Fishery Bulletin 102(1) 



45 N 



40 N 



35 N 



30 N 



140N 



145 N 150 



B 



25 -- 



8> 20 + 



CD 



r =o.20 



15 -I — l — l — l — i — I — i — i — i — i — I — i — i — i — i — I 

 8 10 12 14 

 Mean SST 



Figure 5 



(A) Map to show correlation between sea surface temperatures (SST) and mean fork length (FLl 

 at age for chub mackerel (Scomber japonicus). The dotted area indicates the negative correla- 

 tion coefficient r above 0.4. The contour interval is 0.1 of the correlation coefficient and positive 

 contours are shown as dashes. (B) Relationship between mean SST for the area 38°-40°N and 

 141-143°E from April to June and mean FL at age 0. Correlation was significant at the 5^ level 

 (r=-0.45, n=28, n "=27, df=25). 



To investigate the effect of T and D, we calculated the 

 total effect on k for year-class v according to Sinclair et al. 

 (2002): 



lA^ 



I ft A, 



for T, and 



for D. 



Discussion 



Estimated population abundance of age-0 fish and total 

 biomass may explain density-dependent growth. FL at 

 age 0, 2, and 3 of the Pacific stock of chub mackerel were 

 negatively correlated with the number of age-0 recruits. 

 Correlations between biomass and FL at ages 0-5 were low 

 and not significant. Therefore, year-class strength is indi- 

 cated to have a greater negative influence on the growth 

 of the Pacific stock of chub mackerel than total biomass, 

 as reported for the Atlantic mackerel (Scomber scombrus) 

 (Agnalt, 1989; Overholtz, 1989; Neja, 1995) and Atlantic 

 herring (.CI upea harengus) (Toresen, 1990). 



Density-dependent growth in fish populations seems to 

 be a common phenomenon for pelagic fishes found in the 

 temperate waters of Japan. The FL at age of the 1963-69 

 year classes ranged from 16 to 20 cm, and were smaller than 

 those of the 1970s, possibly indicating density-dependent 

 growth ( Iizuka, 1974 ). According to Honma et al. ( 1987 ), the 

 stock abundance of the Pacific stock of chub mackerel from 

 1963 to 1969 was larger than it was in the 1970s. Wada et 

 al. (1995) and Hiyama et al. ( 1995) found negative relation- 

 ships between total biomass and body length in the Pa- 



cific and Tsushima Current stock of the Japanese sardine 

 (Sarclinops melanostictus). Kishida (1990) demonstrated a 

 density-dependent relationship between the growth and 

 total stock density (CPUE) of Japanese Spanish mackerel 

 (Scomberomortis nipkonius). 



Our results do not agree with the positive effect of sea wa- 

 ter temperature on somatic growth that has been shown for 

 several species, including Japanese common squid (Kidokoro, 

 2001). Atlantic herring ( Moores and Winters, 1981; Toresen, 

 1990). and Atlantic cod (Gadus morhua ) (Brander, 1995; Du- 

 til et al, 1999; Ratz et al. 1999; Otterson et al., 2002). 



