1.3 Scad/Mackerel/Sardine Purse Seine
The sardine and mackerel purse seine net is similar in structure and materials used. For sardines and scad, the net measures 540-720 m long and 108-144 m deep. The mackerel purse seine is 720-900 m long and 126-144 m deep. A deeper net is necessary as mackerel are observed to stay in the deeper layers and are more mobile than sardines and scad. The netting used is knotless nylon with sizes from 210d/9-21 in the body and wing portions and 210d/24-36 at the bunt section. Mesh sizes range from 20 to 33.8 mm at the bunt and 30 mm to 60.9 mm at the body and wing. The selvage uses 210/30 to 210/120, 38.1 and 152.4 mm mesh sizes.
The vessels range from 30 to 150 GT, and normally measure 25 m long, 7 m wide and 3 m deep. They are powered by 300 to 1,200 Hp diesel engines. Electronic navigational and fishing equipment such as radar, GPS, fish finder, SATNAV, sonar, winch and power block are commonly used. In the purse seine fleet, each purse seiner is normally complemented with 3-5 light boats, 1-2 sonar boats and 2-3 fish carriers. In some areas, wooden purse seiners are provided with a “ferris wheel”, an improvised mechanically operated net hauler.
Both net types utilize lights for attraction and sonar for finding fish schools. The lights are of two types; the incandescent 1,000 watts per bulb with 10-12 bulbs per boat and the halogen bulbs with 1,000-5,000 watts/bulb with six to ten bulbs per boat. Lighting operations commences at dusk, and the presence of a fish school is determined by fish finder or sonar. With sufficient fish concentration, the light boat calls the catcher boat, and simultaneously reduces its light to one bulb which is provided with a conical shade to keep the fish school roaming in a smaller radius. The light boat then weight anchor and the catcher boat encircles it.
Using the sonar which can detect and locate fish schools in a 360½ circle around the boat, fish and their abundance are determined. The catcher boat is called for the net setting with close contact and instructions from the sonar boat on both the fish school’s direction, depth and speed.
The net is set around the fish school. In some cases, the sonar boat installs a light on board if the fish school is stationary. The sonar boat is then encircled by the catcher boat until the bottom part of the net is totally closed. The sonar boat moves outside the net and continues searching for other fish schools. The catcher boat hauls the net until the catch is brought on deck for sorting and finally storing in the fish hold. In other hauling operations, the catch is directly guided to a big plastic container and stacked in the refrigerated fish hold.