Sinker for underwater mobile body or sinker for fishing tackle

A fishing tackle having a body and a sinker attached to the body;

• wherein, when the body is pulled approximately horizontally underwater along a flat water bottom within a predetermined speed range, a part of the sinker is kept in contact with the water bottom, and the sinker keeps a curved shape due to water resistance so that a force of pulling the body downward is adjusted in accordance with an amount of the sinker in contact with the water bottom regardless of water depth, thereby being able to keep the body at a constant height range from the water bottom, wherein
• the body is a buoyant body and configured to go underwater while receiving water resistance, and
• the sinker is extended downward from the body and can be freely curved, wherein
• a mass per unit length of the sinker varies continuously, intermittently, or locally in the extending direction,
• excluding a fishing tackle having a sinker whose mass per unit length varies intermittently or locally in the extending direction, due solely to one or more of the following:
• (i) the presence of a component for coupling the sinker to the body;
• (ii) the use of a single type of chain whose mass per unit length varies repeatedly in the same manner in the extending direction;
• (iii) the inclusion of a sinker-release device coupled on both upper and lower sides thereof and designed to cut off and leave the sinker when the sinker snags;
• or (iv) the presence of a component for coupling the sinker-release device to the sinker.