Purse Seining
A salmon purse seiner in Alaska hauling in the net after pursing it - the seine skiff is pulling the seiner away from the net (B. Godfriaux photo)
Link to NJ Fishing Consumer Alert page Link to NJ Fishing Consumer Alert page
Purse seining is a type of fishing in which a long rectangular net with a weighted bottom edge and a buoyant top, floated by the cork line, is run around a school of fish to contain it. As the above photo shows, a smaller boat is used to control the free end of the net until the larger vessel comes around to complete the encircling. At this point a line runs along the bottom edge of the net is hauled in, forming the "purse" by closing of the bottom of the net. This prevents the fish from escaping under the net and they can't get over the floating cork line. 

After the excess net is brough aboard, crowding the fish into a smaller area, they are removed either by brailing - dipping them out with large dip nets called brails - or with fish pumps. 

Because such large nets are used, to the unintiated purse seining generally appears to be an indiscriminate method of harvesting fish. The characteristics of the species sought, however, as well as the knowledge and experience of the fishermen make this an exceptionally clean fishery.  

The primary quarry quarry of purse seiners on the East and Gulf coasts, the menhaden or mossbunker, is a densely schooling fish that forms very compact masses in the water column. Net deployments - called "sets" by the fishermen - on these dense schools contain few if any other species. Periodically other fishermen, disturbed by what they imagine to be large large numbers of non-targetted fish being killed, raise a political ruckus to have what they mistakenly perceive as a  "wasteful" fishery stopped. Then the fisheries scientists dig out the old reports, do some more sampling on the menhaden boats, prove yet again that it's a clean fishery, and go back to their laboratories. 

(Link to article on legislation to arbitrarily restrict NJ menhaden fishingfor an article on an anti-commercial harvesting campaign focusing on menhaden purse seining in New Jersey) 

F/V White Dove Too photo
The purse seiner F/V White Dove Too in Cape May