operated by a mercury switch
When the ring net was shot, the winkie was attached to one end. Once in the water, it would float to an upright position, the mercury would make contact, and the light would come on. Once lit it marked the end of the net in the water; it was often difficult to see and would appear and disappear on the waves. The name winkie most probably comes from the blinking action as perceived by the onlooker.