Glaucus an autonomous net, manages fish stocks sustainable and controlled by the connection with a monitoring system. An overfishing is avoided. A special selection ensures that in the future more fish can swim in the sea. By large mesh openings of conventional trawls big amounts of by-catch and unwanted fish size reach on the ship, which are usually thrown dead overboard. Glaucus, which is equipped with the latest sonar and sensor technology, is left in fishing area into the water and searches autonomic for fish. It encircles a school of fish with air bubbles, counts them and determines fish species and sizes by their silhouettes. At high by-catch, the process will be cancelled and the fish will set free. The 3-zone-selection sorts different size of fishes by sorting grids with variable mesh sizes. By the sorting grids, large individuals can not enter the net body, otherwise they will be freed separately through an aperture at the Selection Rings.