Seines, purse seines and lift nets
Fish which swim in schools through the water column can be caught efficiently with seines. A seine net is a very long net, with or without a bag in the centre, which set either from the shore or from a boat for surrounding a certain area and is operated with two (long) ropes fixed to its ends (for hauling and herding the fish). One end of the rope has a buoy attached to to it. The buoy, the first rope, the net and the second rope are released consecutively as the ship returns in a large circle to the buoy. From that point the net is then hauled. Purse seines are an active fishing method targeting pelagic species. Purse seines are large netting walls set for surrounding aggregated fish both from the sides and from underneath, thus preventing them from escaping by diving downwards. Purse seines can be large or small. Lift nets are often square nets attached to crossbars. Where the bars cross a line is attached to move the net vertically from a boat or from the shore. The net lays on the bottom and is quickly hauled after some time. The fish above the net will then be caught. Depending on the target species, lamps or bait can be used to attract fish.
Danish seines are a small-scale variant of the bottom seine fishery and is also called snurrevaad. Danish seines are bag shaped nets with long ropes. Danish seines anchor their buoy and the ship doesn’t move while hauling the net. This traditional method of seining is therefore also called anchor seining. A potential negative impact is the bycatch of undersized fish and non-target species.
Purse seines are an effective method to catch fish swimming in schools in the watercolumn. The fishermen set the net around a school of fish. The net is then closed from underneath and hauled. A purse seine is used to catch pelagic fish, like herring and mackerel. The bycatch depends on the target species. Purse seines vary from small to large (approximately 150 meters high to 500 meters wide). The fuel use is low and there is no impact on the seabed. Bycatch can be a large problem, especially in the tuna fishery.
Purse seine with FAD
Fish Aggregating Devices (FADs) are floating objects like buoys or floaters which use the attribute of many fish species to school around floating objects. When there is enough fish around the FAD the purse seine is employed to catch everything. Advanced FADs have sonar and GPS, so the fishermen can see where the FADs are and how much fish is aggregated. Because tuna schools with other (tuna)species, there is a lot of bycatch including sea turtles, rays, sea birds and sharks.
Purse seine without FAD
Because Fish Aggregating Devices (FADs) have a lot of bycatch of sea turtles, rays, sea birds and sharks, the alternative of not using FADs is a more sustainable fishing method.
The lampara net is a surrounding net, shaped like a dust pan or a spoon (the leadline is much shorter than the floatline) with two lateral wings and a central bunt with small meshes to retain the catch. After the ship has moved in a circular motion, both wings are hauled simultaneously.
Scottish seine nets are very long nets, with a bag in the centre, which set either from the shore or from a boat for surrounding a certain area and is operated with two long ropes (seine ropes) fixed to its ends (for hauling and herding the fish). One end of the rope has a buoy attached to to it. The buoy, the first rope, the net and the second rope are released consecutively as the ship returns in a large circle to the buoy. From that point the net is then hauled. The ship moves slowly forward while hauling the net. Dutch fishermen target gurnard, mullet, squid and plaice with this method. This technique has less impact on the seabed than bottom trawls and a low fuel use.
A beach seine is a seine net operated from the shore. The gear is composed of a bunt (bag or lose netting) and long wings often lengthened with long ropes for towing the seine to the beach. The headrope with floats is on the surface, the footrope is in permanent contact with the bottom and the seine is therefore a barrier which prevent the fish from escaping from the area enclosed by the net. Target species are mainly demersal fish. A (potential) negative impact of beach seines is bycatch due to the use of too large nets or too small mesh sizes.
Boat-operated lift nets
Lift nets are often square nets attached to crossbars. Where the bars cross a line is attached to move the net vertically from a boat or from the shore. The net lays on the bottom and is quickly hauled after some time. The fish above the net will then be caught. Depending on the target species, lamps or bait can be used to attract fish. Boat-operated lift nets can be hauled manually or mechanically. ift nets are hauled out by hand or mechanically. For operating a large lift net and maintain it open, several long poles off one or the two sides of the boat are, in general, necessary. A number of pulleys and/or small winches for letting the lift net to dip, then for the hauling of it. The unwanted bycatch is low, but lamps attract multiple species.
Vanaf de oever bediende kruisnetten
Lift nets consist of a horizontal netting panel framed by wood or metal bars or a bag shaped like a parallelepiped, pyramid or cone with the opening facing upwards. Stationary lift nets are operated usually form the bank of a river or a suitable beach by installing them on a special platform. The more modern lift nets are operated with the help of hand or motor driven winches.