Seasonal changes in age composition and growth of Spanish mackerel landed in Ehime Prefecture from Iyo-nada of the Seto Inland Sea

Abstract

To examine seasonal changes in age composition and growth of Spanish mackerel Scomberomorus niphonius landed in Ehime Prefecture from Iyo-nada, Seto Inland Sea, the fork length of 11,058 fish was measured at the Kaminada Fish Market from 2000 to 2006. Monthly compositions of the fork length were then obtained, which were decomposed into size (age) groups by fitting the normal distribution curves. Based on otoliths examinations from 1,399 samples, age specific mean fork lengths and their standard deviations were estimated and used as the initial inputs for the normal curves. Age composition in spring (March–June) mostly consisted of 2-year-old fish and some 1 and 3-year-old fish, while that in autumn (August–December) mostly of 1-year-old fish with 0-year-old fish occurring in November and December. Monthly growth rate of the fork length was high from summer to autumn and low from winter to spring.