See also otter trawl, trawler. "The rollers along the bottom of the net were replaced by 'rockhoppers,' large disks that tend to hop up when they hit a rock and make it possible to drag close to a rough ocean bottom without damaging the net. In addition, 'tickler chains' stir up the bottom, creating noise and dust. Cod, and other groundfish, instinctively hide on the bottom when they sense danger, and the ticklers act like hunters beating bushes to drive birds out, sending the frightened cod out of their protecitve crannies and up into the nets.
"The ocean floor left behind in a desert. Any fish swimming in the vast area of these nets is caught. The only control is mesh size... but fishermen often point out that once the back wall of the cod end has a good crop of fish in it, few fish of any size can escape, regardless of how big the mesh. Millions of unwanted fish... are tossed overboard, usually dead." —Mark Kurlansky, Cod: A Biography of the Fish That Changed the World (New York: Penguin, 1997), 140–141