Commonly used for the commercial harvesting of scallops, clams, oysters and mussels, a dredge consists of a metal rectangular frame to which a bag-shaped net of metal rings has been attached.

The frame's lower end is called the raking bar and is often equipped with metal teeth used to dig up the bottom. The frame is connected to a towing cable and dragged along the sandy floor, much like a trawl net.

Variations include hydraulic or jet dredges, which use pressurized water pumped from the vessel to stir up deep-burrowing clams, and suction dredges, which use pump-driven suction to suck the shellfish up a pipe to the boat.