Watanabe and Yatsu: Interannual variation in length at age of Scomber japonicus 



197 



45°N 



40 C N 



35°N 



30°N - 



Kuroshio-Oyashio transition zone 



izu Islands 



— i 



130°E 



140°E 



150°E 



160°E 



Figure 1 



Distribution of the Pacific stock of chub mackerel (Scomber japonicus) 

 and major oceanographic features around Japan. The hatched areas show 

 spawning grounds. The dotted areas show feeding grounds. Major purse-seine 

 fishing grounds are surrounded by dashed lines. The fishing grounds around 

 the eastern coast of Hokkaido failed in 1977 with the decline in biomass 

 (Hirai, 1991). 



this study we describe the variation in FL at age of the 

 Pacific stock of chub mackerel in the Kuroshio-Oyashio 

 area, using data from 1970 to 1997 when the stock biomass 



fluctuated between 0.2 and 5.9 million metric tons. We use 

 these data to evaluate the effects of population density and 

 sea surface temperature on FL at age. 



