An Analysis of Determinants of Consumer Prices for Mackerel: Evidence from Size Composition and Import Prices

This study examines why mackerel consumer prices in Korea have remained elevated despite increases in aggregate production, focusing on size composition and import prices. A first-differenced distributed lag model with Newey-West HAC standard errors is estimated using monthly data from January 2019 to December 2025. The increase in production was concentrated in small-sized fish, while the supply of medium- and large-sized fish destined for food consumption declined substantially. When total production and medium- and large-size production are entered jointly, the cumulative coefficient on the latter over lags of zero to three months remains negative and significant, whereas no additional contribution from total production is detected. Decomposing total production into a scale effect and a composition effect shows that the two moved in opposite directions, so that the aggregate indicator conflates them. Import prices co-move with consumer prices contemporaneously, but no significant cumulative pass-through is found. These findings are consistent with the notion of a “total production illusion”, in which total output overstates effective food-use supply. The analysis identifies the direction and lag structure of these associations rather than causal effects, and suggests complementing supply-demand management with size-specific supply indicators.