In Anamizu and Nanao Bay, it was common to see these little watchtowers called "bora-machi yagura" or mullet fishing tower (ボラ待ちやぐら). An ancient fishing method to catch mullet.

There's a fishing net laid on the bottom of the shallow water. A fisherman sits on the tower and watches for mullet swimming over the fishing net. He then pulls up the net.