I have commercial fished for Menhaden since 1981 as a crewmember and since 1997 as a Captain on the East Coast and Gulf of Mexico. Setting a purse net and retrieval of the net is an art.Not only do you have to catch the fish you also have to not destroy it. The winches that are used are called pursing units. They can be sped up or slowed down to adjust the bottom of the net from making contact with the bottom. If the nets were to stay on the bottom every set the net would be destroyed evey set. Every Captain  is a very proficient at deployment of their nets. If they weren't,they wouldn't be a Captain.