Growth of juvenile chub mackerel Scomber japonicus in the western North Pacific Ocean: with application and validation of otolith daily increment formation

The growth of juvenile chub mackerel Scomber japonicus collected in the western North Pacific Ocean in 2007 and 2009 was examined based on the evidence of otolith daily increment formation in captive specimens. There was a significant difference in the relationship between known age and number of increments in the frontal and sagittal planes. Repeated markings on the otolith using Alizarin complexone and the coefficient of variation in number of increments suggest that the increments in the frontal plane of the otolith are more suitable for age estimation than those in the long and short axes of the sagittal plane. The increments in the frontal plane formed daily, and the first ring was usually deposited 3 days after hatch. Age of wild juveniles ranged from 24 to 211 days after hatch based on the frontal plane method. The estimated hatching periods of specimens ranged from February to June, but the April-hatched specimens were collected throughout the sampling periods of 2007 and 2009. The Gompertz growth model showed a difference in growth pattern in specimens between 2007 and 2009. The juveniles in 2009 appeared to grow more quickly than those in 2007 until summer, but thereafter the 2009 specimens seemed to grow more slowly.