太平洋岸域のカタクチイワシの資源回復に伴う２〜３月産卵量の増加

Abstract

Stocks of Japanese anchovy Engraulis japonicus have been recovering since 1990 along the Pacific coast of Japan. The annual egg production in the Pacific side of Japan increased from 710 trillion eggs in 1980 to 5721 trillion eggs in 1991. The late winter (February and March) egg production increased from 10 trillion eggs in 1980 to 359 trillion eggs in 1993. The areas of the spawning ground of Japanese anchovy in late winter increased from 76000km2 in 1980 to 220000km2 in 1991. The spawning grounds in late winter expanded from the waters on the continental shelf to the Kuroshio current. The increase in the late winter egg production and spawning ground was related to the increase in the winter adult population, which migrates from the northern waters of the Pacific side of Japan to the southern waters in late winter. The stock size (Y) was positively correlated with the egg production in February plus March (X1) or the area of spawning grounds in February plus March (X2): Y=0.94 X1+71.7 (r2=0.91, p<0.01); Y=15.5 X2+4.5 (r2=0.72, p<0.01). The rough stock size of anchovy can be estimated using these regression expressions.