Effects of temperature and food availability on growth rate during late larval stage of Japanese anchovy (Engraulis japonicus) in the Kuroshio-Oyashio transition region

During periods when the population size of Japanese anchovy Engraulis japonicus is large, the abundance of 1-yr olds has been considered to be dependent on the growth and survival processes in the late larval and early juvenile stages in the Kuroshio-Oyashio transition region off northern Japan. Recent growth rates for 10 days before capture of larval and early juvenile E. japonicus were estimated and examined in relation to the surface water temperature and the available copepod density in 1997, 1998 and 1999. Late larval and early juvenile E. japonicus were distributed in the waters with temperature from 15 to 19 degrees C and available prey density from 10 to 1000 mg dry weight (DW) m(-2) in the transition region. The late larval growth rates were found to be regulated more strongly by water temperature than by copepod density in the waters < 16 degrees C, and more strongly by copepod density than water temperature in the waters < 100 mg DW m(-2) in the Kuroshio-Oyashio transition region. The recent growth rates decreased from the western waters to the eastern waters in the survey area 140-170 degrees E in 1998, correlating with decreases of food availability to 50-100 mg DW m(-2). While in 1999, the recent growth rates were faster in the waters east of 150 degrees E, resulting from eastward expansion of warm water ranges and high available prey density 100-400 mg DW m(-2). The key environmental factors regulating late larval growth rate of E. japonicus in the transition region seem to be spatially different between years.