Dredge

This diagram from the 19th century depicts a dredge for catching oysters. The dragnet of a dredge is attached to a rigid frame that is hauled over the seabed. This ploughs up the seabed in order to flush muscles and other shellfish, which are buried in the seabed, into the net. Dredges are now controversial, as their use can damage the seabed.

An oyster dredge at work, drawing, 1874–1875, artist unknown; source: Wikimedia Commons, http://commons.wikimedia.org/wiki/File:PSM_V06_D020_An_oyster_dredge_at_work.jpg, Popular Science Monthly 6 (1874–1875), p. 10, https://archive.org/details/popularsciencemo06newy, digital copy: archive.org, public domain.