Fishing Equipment used by High Seas Fisheries
Gillnets
Gillnets are used worldwide, but because of their indiscrimination of what they catch, they have been banned in most developed countries. A gillnet, also known as an entanglement net or a trammel net (when three gillnets are combined with different mesh sizes to catch more), are set as a vertical wall into the water column. Nets have floaters on the head rope and weights on the foot rope and because of this the buoyancy of the net can be adjusted to allow the net to be placed at the surface, mid-water, or the bottom as pictured. The idea with these nets is to set a long line of them drifting in the water anchored to the sea floor and capturing anything that fits in the mesh, where they are either gilled or entangled. There is a difference between entanglement and being gilled, entangled means that a body part has been tangled in the net, while a gilled fish is only caught by its gills. This method of fishing has a wide variety of impacts, as mentioned is not very selective and endangered species such as turtles and sharks can become easy caught. There is also a worry about "ghost fishing" where lost nets will continue to drift and entangle creatures.
Trawls: Mid-water and Bottom
Mid-water trawl nets have a cone shaped body, normally much larger than bottom trawl nets. Near the opening, the mesh is bigger to corral fish to the center and mesh gets smaller to ensnare the fish at the back. Lateral wings spread out from the opening with weights attached to keep the mouth of the net open as it travels. A sensor may be attached to the net to give the crew an idea how far from the surface and the bottom the net is and the concentration of fish in front of the net opening. Bycatch is relatively low compared to other methods especially when implementing exclusion devices. And if used properly there is no threat to bottom habitats. Bottom trawl nets are also cone shaped ending in codend where bottom fish are held. There are three types of nets, depending on how the mouth is kept open. There is the bottom otter trawl that uses two heavy doors to keep the net on the bottom and the mouth open. The beam trawl rarely has wings to keep the mouth open since a set of bars keeps the mouth rigidly open. And finally there is the bottom paired trawl, where a trawl net is pulled behind two boats to keep the mouth open. The ground line is usually equipped with tires to keep the trawl from snagging. The impact of bottom trawls on the environment causes damage to anything sedentary organisms, such as corals. Bycatch consists of organisms that can't get out of the way of the trawl and are normally discarded at sea.
Hook and Lines
This gear uses natural or artificial bait to attached fish to be caught on metal hooks attached to a line. This method can be done with single hooks attached to a pole or just on a line. There can also be multiple lines set out with many baited hooks attached. Impacts of using this method are limited to bycatch. Hooks can be baited to try to go after a certain species, but opportunistic organisms, such as birds and some sharks, can be caught.
Purse Seines
Purse Seines, also known a surrounding net, are basically vertical nets that are pulled to encircle a school of fish and the bottom is closed off by pulling an a couple pieces of rope, just like a purse bag, to keep the school from escaping by diving. The fish are then pulled on board to be processed. This is a surface net and is a large part of the tuna fishery. The biggest concern when fishermen used these nets was the accidental bycatch of dolphins by tuna fisheries. For more on this click here.