A trawl is a large, bag-shaped net that is towed by a fishing vessel. Trawlers are generally large boats ranging from 70 feet to over 200 feet in length. The doors, because of the way they are built and rigged to the trawl, keep the mouth of the trawl open as it moves through the water. The headrope is equipped with floats forming the upper opening. The footrope is rigged with weights forming the lower opening. Trawlers use sophisticated ultrasonic devices both for location of fish underwater and for species identification. Pelagic trawls sometimes contact the ocean bottom, but their heavy doors and wires are kept off the bottom to avoid damage to benthic habitat.
Fishing with pelagic trawls is a selective method of fishing, because the nets can be operated in ways to minimize the incidental catch of non-target species. Pollock are usually harvested with few other species. Sole are generally captured in bottom trawls in mixtures of the various species which are sorted onboard the fishing vessel. Trawling is allowed only in certain areas and strict limits are enforced upon the amount of non-target species (such as crab or halibut) that may be caught. In fact, it frequently happens that a trawl fishery is closed because it reached the pre-set “bycatch” limit, and does not achieve full harvest of its target species.
Fishing with pelagic trawls is a selective method of fishing, because the nets can be operated in ways to minimize the incidental catch of non-target species. Pollock are usually harvested with few other species. Sole are generally captured in bottom trawls in mixtures of the various species which are sorted onboard the fishing vessel. Trawling is allowed only in certain areas and strict limits are enforced upon the amount of non-target species (such as crab or halibut) that may be caught. In fact, it frequently happens that a trawl fishery is closed because it reached the pre-set “bycatch” limit, and does not achieve full harvest of its target species.
Once the trawl full of fish reaches the surface of the water, one of two things happens. If the vessel has the ability to process the fish onboard, it is called a factory-trawler or a freezer-trawler or catcher-processor. These vessels simply pull the net aboard, empty the net, sort the species, and process the catch. If the vessel is only capable of catching fish, then it must deliver the catch to a processing plant. These processing plants might be in other vessels, called floating processors, or they might be on shore.
The only legal fishing method for halibut is longline gear. Longline fishing is also often used for harvesting sablefish and cod, but never for pollock or sole. Longline fishing vessels are usually independently run by owner-operators. Some longliners are small boats, less than 50 feet in length, but most are somewhat larger. Longline gear is composed of groundline, buoy lines, and gangions, which are short pieces of line with hooks on the end.
Longlines are set along the seabed, with baited hooks every few yards. Longline hooks are retrieved one at a time. The fishermen can unhook other species of fish and return them alive to the sea without bringing them on board. In this way, longlining is considered a style of fishing with very little bycatch.
The third type of fishing gear used to catch Alaska whitefish is pot gear. Pots are used only for sablefish and cod, never for pollock, halibut, or sole. Pots are large steel-framed cages covered in net mesh. The baited pots are placed on the seafloor where they trap the fish.
Fish enter the traps through tunnels but cannot escape. Later the pots are retrieved and the fish are sorted on deck. Non-target fishes are returned alive to the sea. In contrast to years past, very little fishing gear is lost at sea.
The old problem of “ghost gear” (lost gear that continues to fish) has essentially disappeared.
Because of improvements in cables, net materials, and fishing methods, the loss of a trawl is a very rare event. Pots must have biodegradable panels which allow fish to escape in the event that a pot is lost. Important changes in fishery management regulations allow longliners to fish at a slower and safer pace, so they can avoid setting more gear than they can recover. There are also strict rules in place to prevent seabirds from being accidentally caught in longline gear.