For half a century, Takeo Nakajo has been catching katsuo, or skipjack tuna — indispensable in Japanese cuisine whether eaten raw, dried or used as a base for the broth. But he and other fishermen in Kure, in Kochi prefecture in southwest Japan, have seen something worrying in the past two years — an unprecedented number of unusually fatty katsuo. While heavier katsuo means more money, locals and experts say it indicates climate change and a risk for katsuo numbers already under threat due to growing demand and overfishing. “The fatty katsuo must have something to do with the water temperature,” said the