Tuna once completely disappeared from the Tsugaru Strait where fishermen had enjoyed bumper catches before. But, the tuna fishing has been reviving and enriching the life of the neighboring fishermen since a couple of years ago in the Tsugaru Strait, especially at Oma. Why then was the tuna population dwindling in the strait for over twenty years? I consider this phenomenon to be tied to the progress of the Seikan Tunnel.