Commercial Fishing, Sustainability and Environmental Impact

Commercial Fishing
Longlining

Longlining —> Longlining is one of the most productive methods of catching fish. Lines of varying lengths, some as long as 50 miles, are rigged with baited hooks at set intervals throughout the water. Bottom fish such as cod, halibut, and monk fish are caught with anchored lines set horizontally and are marked with surface buoys for Tuna and Mahi Mahi, whereas swordfish lines are set closer to the surface.

Horizontal lines are also employed and anchored to the bottom and buoyed on top. Longlining is a controversial fishing method because it indiscriminately catches unwanted fish species as well as marine mammals and birds, in particular the albatross. Methods deemed friendly to sea birds include fishing at night and setting streamers on the lines to scare the birds away. Eliminating, minimizing, or utilizing waste from fish fabrication is another step in the right direction. New methods are turning the fish by-products into usable fish meal on board the vessel. This encouraging development goes a long way toward true sustainability.

Gillnetting

Gillnetting —> Gill nets are long walls of nets set close to or below the surface, on the bottom, or at various depths depending on species and location. They can be easily located along a known migration path to catch large quantities of fish. Varying in mesh size, these nets are invisible to the fish as they swim into them. Once their heads and gills go through the net, they become entangled and die, which drastically affects the quality of the fish, so speed in harvesting is essential.

Drift Nets

Drift Nets —> Trapping fish in the same way as gill nets, drift nets are not affixed to anything and silently move with the tide, entangling the fish. Used at sea to catch squid, tuna, salmon, and other valuable species, these nets have prompted the United Nations to recommend a global moratorium on large-scale high-seas drift netting to protect the large pods of dolphins and turtles from becoming entangled in nets up to 3,000 yards long.

Easily lost, and invisible, they are referred to as ghost nets; they drift and fill up with fish until the weight causes them to sink to the bottom of the sea. Once the entangled fish are consumed by other marine life, the net floats back up to the surface repeating the process. Unfortunately, modern nylon nets do not disintegrate but stay intact, rising and falling in the sea. A disadvantage of both drift and gill nets is the indiscriminate catch of species.

Trawling

Trawling —> Trawling is a method of fishing that pulls different sized nets through the water to capture various species of fish and shellfish. Boats can operate in tandem, pulling large nets through the water, or a single vessel can use a beam, which holds the net open as it is dragged along the ocean bottom or at various depths. Bottom trawlers have chains attached that stir up the seabed and force ground fish up into the waiting net. Trawling nets are controversial because of the damage they cause to the ocean floor.

Midwater trawling deploys a large cone-shaped net from the stern of the boat and pulls it through the water scooping up anything in its path.  Once full, the net is hauled onboard and the fish are placed in the hold. Unwanted bycatch and damage to the fish as they are lifted onto the vessel are disadvantages of this method.

Trolling

Trolling —> Trolling utilizes lures or baited lines from the stern of the boat to capture valuable game fish such as Tuna, Mahi Mahi, and Sailfish. Weights are connected to wire lines with 15 to 20 leaders, each of which is pulled behind the boat. Each line can also be rigged individually and winched in to quickly recover the fish alive. This method is especially beneficial for Tuna because their body temperature can increase drastically during the fight and proper bleeding and immediate cooling are important to the value of the fish. Fish can also be more easily targeted by utilizing specific jigs and live bait.

Purse Seining

Purse Seining —> Purse seining encircles schools of fish with a wall of net that is then pursed (drawn together) on the bottom, trapping the fish. The entire net is brought to the side of the vessel and the fish are pumped or scooped onboard. Targeting large shoals of Tuna and Mackerel, this method became controversial in the 1970s when dolphins were deliberately encircled to facilitate catching the Tuna with which they congregated.

Fish Traps or Pots

Fish Traps or Pots —> Lobster, crab, and fish are caught using various sized pots made of wire, metal, wood, and line. The pot is baited, thrown overboard, and sits on the bottom attached to a buoy. The entrance is designed to prevent escape from the trap. An advantage of this method is that it is highly selective; everything is caught alive with little or no bycatch or habitat destruction. Pot sizes vary; with Alaskan red crab, pots are able to hold hundreds of pounds of crab. Fish traps are especially popular throughout the warm calm waters of the world for their ability to catch specific varieties of fish.

Dredging

Dredging —> Primarily used for shellfish such as clams, scallops, mussels, and oysters,a dredge is a metal basket with a type of rake or teeth assembly that aids in removing mollusks from the seabed. Clam dredges at sea are very large and must be towed from a sizable vessel. Modern dredges pump pressurized water in front of the rakes to loosen the silt and churn up the shellfish. Towed from bars off each side of the boat, the number of baskets or dredges deployed from a single vessel may reach several dozen depending on the catch. Dredging is controversial because it can tear up and disrupt the sea bottom, as well as have a negative effect on the natural sediment of the spawning habitat of shellfish.

Divers —> Divers utilizing scuba gear, or air pumped from the surface, collect a wide range of shellfish from the sea bottom.  Scallops collected this way are referred to as day boats because the divers harvest and return on the same day. Due to the high cost of harvesting, these items command a premium market price.

Sources —> “Kitchen Pro Series: Guide to Fish and Seafood Identification, Fabrication, and Utilization.” Culinary Institute of America (CIA), Mark Ainsworth. 2009.

Diagrams —> https://www.msc.org/home

Photographs —> © Mark Peterson

Alaskan Salmon Purse Seining

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A purse seine is a large wall of netting deployed around an entire area or school of fish.

The seine has floats along the top line with a lead line threaded through rings along the bottom. Once a school of fish is located, a skiff encircles the school with the net. The lead line is then pulled in, “pursing” the net closed on the bottom, preventing fish from escaping by swimming downward.

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  • Purse seines can reach more than 6,500 ft (2,000 m) in length and 650 ft (200 m) in depth, varying in size according to the vessel, mesh size, and target species.

  • Finding a school of fish is one of the most difficult steps of this fishing technique and include:
    • Natural cues such as a congregation of seabirds, ruffling of surface water and/or fast moving groups of dolphins.
    • Helicopters scanning the water for natural cues from the air to direct boats toward schooling fish.
    • Using radar fish finders to help identify the exact location and size of a school.

There are other types of catching salmon such as gill netting and trolling employed in Alaska and other American coastal waters.