The marine biology dredge is used to sample organisms living on a rocky bottom or burrowing within the smooth muddy floor of the ocean (benthic) species. The dredge is pulled by a boat and operates at any depth on a cable or line, generally with a hydraulic winch. The dredge digs into the ocean floor and bring the animals to the surface where they are caught in a net that either follows behind or is a part of the digging apparatus.
Early dredging samplers did not have a closing device, and many organisms were washed out. This led to a mistaken impression that the deep-sea bed lacked species diversity, as theorised by Forbes in his Azoic hypothesis. Later samplers devised by Howard L. Sanders and the Epibenthic sled designed by Robert Hessler showed that deep-sea bottoms are sometimes rich in soft-bottom benthic species.