We went back to Arashiyama last night and rode one of the boats to get this close up shot of the cormorant birds (Ukai) in action.
The fisherman has five cormorants on leashes, and watches them in the water. The fire attracts the fish, so the birds can easily catch them.
But why don't the cormorants eat all the fish? There is a ring, loosely tied around their necks; they can swallow smaller fish but not the larger ones. The fisherman pulls the bird into the boat and disgorges the larger fish from their beak. So the cormorants get an easy dinner and the fisherman gets the largest ones.
More on this ancient style of fishing on Wikipedia...