A fishing dredge, also known as a scallop dredge or oyster dredge, is a kind of dredge which is towed along the bottom of the sea by a fishing boat in order to collect a targeted edible bottom-dwelling species. The gear is used to fish for scallops, oysters and other species of clams, crabs, and sea cucumber. The dredge is then winched up into the boat and emptied. Dredges are also used in connection with the work of the naturalist in marine biology, notably on the Challenger Expedition.