Dictionary of Ichthyology  

trawl = a bag-shaped net towed behind a ship either along the sea floor or in midwater, having a buoyed head rope and a weighted foot rope to keep the net mouth open. It may be towed by one or two ships (here by sail in the nineteenth century).

From Whymper's "The Fisheries of the World", 1883. Photograph by Brian W. Coad.

Canadian Museum of Nature