Bonito tuna prices were around JPY 1700 (USD 14.09, EUR 12.43) per kilogram at Tokyo’s Tsukiji market in the first week of September, about 20 percent off the same period last year. Fatty bonito have returned to northern Japan’s waters earlier than usual, due to higher water temperatures presumably connected with global warming.

Bonito move to the northern Pacific in the spring, returning south in autumn much fattier. The main ports of landing are currently in Miyagi and Iwate Prefectures i…