Ekman type dredge. Open (left) and closed (right). 1930s.

This dredge was designed by the Swedish oceanographer Sven Ekman (1876-1964) to sample soft bottoms. Many variants of this device have been created. Before sampling the mouth is kept open by two ropes blocking the dredge jaws to a release mechanism. By exerting pressure on the arm to which the dredge is attached, or by sending a messenger, the jaws are released and can close drawn by a spring, trapping the surface of the bottom sediment.