A lot of by-catch is caught in gill nets.
Gill nets ‘stand’ upright on the seabed thanks to floats on the top and lead weights on the bottom. The fish are caught when they become entangled in the nets. Gill nets come in various mesh widths, constructions and dimensions, each targeting a specific type of fish. By far the most common type of gill net in the Netherlands is a net designed to catch sole. The nets are made of relatively fine mesh and are about a metre in height. The relatively small number of floats keeps them upright and curled on the bottom.
Foreign data indicates that this type of net is responsible for relatively little by-catch. Drift nets with large mesh seem to give more by-catch, such as the nets used for catching cod, turbot and brill. Drift nets are widely used in the Danish fishing industry. The number of porpoises caught there as by-catch in the North Sea over the last decade is estimated at around six thousand per year (Vinther and Larsen 2004), most of which become trapped in large-mesh nets.