Life history patterns of Japanese eel Anguilla japonica in Mikawa Bay, Japan

The otolith microchemistry of female Japanese eels Anguilla japonica collected in Mikawa Bay, Japan, in June 1998 to June 1999 was examined with an electron probe microanalyzer. Total length ranged between 62.0 and 96.0 cm, and body weight between 291 and 2057 g. Gonadosomatic index (GSI) increased from less than 0.2 in August to greater than 4.0 in January Temperature of the sampling site ranged between 6.6degreesC and 28.8degreesC, and salinity between 24.6parts per thousand and 32.7parts per thousand. Otolith Sr:Ca indicated that the life history patterns of eels could be classified into three types: Type 1, Sr:Ca from approximately 150 mum from primordium to edge of the otolith maintained at the level of approximately 0-4 x 10(-3), indicating that eels after the elver stage stayed in fresh water until the silver eel stage; Type 2, the ratios were 4-10 x 10(-3), indicating that eels stayed in seawater from elver stage to the silver eel stage; Type 3, the ratios fluctuated between those of Types 1 and 2, indicating that eel migrated between freshwater and seawater before the silver stage. Results suggest that the growth phase of yellow stage Japanese eel does not have definite habitat selection and that the population is predominately estuarine.