Bull. Jpn. Soc. Fish. Oceanogr.74(2), Page 81-87, 2010   Examining a possibility of forecasting the Spanish mackerel catches in Ehime Prefecture from Iyo-nada Masamitsu Chiba1†, Toshihiro Katou2, Yoshimi Kouno1 and Shin’chirou Seki1 1 Ehime Prefectural Research Institute of Cultivation Resources, Mori, Iyo, Ehime 799-3125, Japan 2 Ehime Prefectural Office Fisheries Promotion Division, Ichibancho, Matsuyama, Ehime 790-8570, Japan †e-mail: chiba-masamitsu@pref.ehime.jp To examine the possibility of forecasting the Spanish mackerel Scomberomorus niphonius catches in Ehime Prefecture from Iyo-nada, Seto Inland Sea, the fork length (FL) of 13,983 fish was measured at the Kaminada Fish Market from January 2000 to June 2008. Monthly compositions of the FL were then obtained, which were broken down into size (age) groups by fitting normal distribution curves. Based on the monthly catch, age compositions and relational expression of FL and body weight, the catch number by landing season and year class were estimated. It was considered that abundance of this species in the biomass/population of the 1999 year class was large, whereas that in the biomass/population of the 2001 year class was small. A negative correlation between the FL of age 1 at spring and the catch (individuals) of “Sawara” brand (age 1 at summer, autumn, winter and age 2 at spring) was observed. After 2000, a positive correlation between the catch in Iyo-nada and the catch of the previous year in Uwa-kai, Bungo Channel was observed. These results suggest that the FL of age 1 at spring and the catch of the previous year in Uwa-kai can be used to forecast the Spanish mackerel catches from Iyo-nada. Key words: Spanish mackerel, Iyo-nada, landing forecast