In this study, I use a mathematical method to analyze changes in edible seaweed production patterns over 60 years in each seaweed-producing prefecture in Japan, by using annual fishery records. Production trends were analyzed using parsimonious regression models of increasing order for: an intercept-only model, a linear model, a quadratic model, and a cubic model. Based on the chosen model parameters, seaweed production trends were classified into three main categories: collapsed, stagnating, and increasing. The results show the spatial pattern in long-term temporal trends of production, which are classified in three main categories: increasing, stagnating, or collapsed. Since 1956, seaweed production in Japan has decreased at a rate of more than 3,600 tons. Production has collapsed in 90% of the seaweed-producing prefectures, and this pattern has been observed after 1970 for 66% of the prefectures. The results also indicate that the production loss in Japan Archipelago extended from north to south and from ocean-side to inland sea-side areas. This study demonstrates that seaweed production loss has been registered in Japan in the last 60 years, therefore new investments and strategies to maintain production in the high-performing areas are required.