Otter Trawl Net
This diagram shows how an otter trawl works, with towing lines (or warps) from the trawler going to the otter boards or doors, which hold the net open. The net drags along the bottom when catching ground fish, and the caught fish collect in the cod end of the net. The net is hauled back to the trawler every few hours and emptied.
Otter trawls can be used for midwater species, and sometimes two ship share the towing in what is called pair trawling.
This drawing is by Robin Amaral for an article "Bottom Tending Gear Used in New England" by Ronald Smolowitz and published in an MIT Sea Grant publication, Effects of Fishing Gear on the Seafloor of New England.