Fishermen use a wide range of gear to land their catch. Every type has its own effects on the ocean. By selecting the right gear for the right job, the fishing industry can help minimize its impact on the environment.
Beach and Boat Seines
Seines are long nets, with long ropes on each end, which herd fish when dragged or towed. They’re hauled over sandy or muddy bottom habitat, and the cloud of sediment helps herd the fish into the net. Seines are suspended vertically in the water with floats and weights, and some have a bag for catching fish. Beach seines are hauled in from the shore and are used to catch species like Atlantic croaker, Florida pompano and striped mullet. As the name implies, boat seines haul the catch onto the vessel. Danish seines, also known as "anchor seines," are a type of boat seine. The catch of unwanted species can be an issue in these fisheries.
Bottom trawls are cone-shaped nets that are pulled along the seafloor by one or two boats to catch cod, halibut, lobster, rockfish, shrimp and other bottom-dwellers. The variety and amount of non-targeted ocean life that’s caught in many bottom trawl fisheries is a pervasive problem, and the heavy gear can damage sensitive seafloor habitat. Reducing the harmful effects of bottom trawling requires limiting when and where trawling can occur and gear modifications that allow unwanted marine life to escape and lessen impacts on the seafloor.
Dredges are metal-framed baskets that are dragged across the seafloor to collect clams, cockles, mussels, oysters, scallops and sea cucumbers. Towed dredges scrape or dig into the substrate with rakes or teeth to about a foot in depth. Mechanized dredges are used to dig and wash out mussels that have buried into the seabed. There are also hand-held dredges. This fishing method can have significant impacts on sensitive seafloor habitat and bottom-dwelling species. One way to limit these harmful effects is to limit the areas where dredging can occur.
Gillnets are walls of stationary or drifting netting that are almost invisible to fish, so species like cod, perch, salmon, sardines and trout swim right into them. Set, drift and trammel gillnets use different configurations of floats and weights to suspend the netting more or less vertically. Encircling gillnets are set in shallow waters, and noise or another means is used to entangle the fish in the netting. Fix gillnets are stretched between two or more stakes that are driven into the seabed in the intertidal zone. Gillnets can accidentally catch vulnerable ocean animals like sea turtles, marine mammals and sharks. These impacts can be reduced by setting the gillnets deeper in the water column to allow room for animals to swim over and adding gear like pingers, which warn passing marine mammals.
Handlines and Jigs
Handlines are used to catch species like tuna, snapper and grouper. They can be a single fishing line, hook and bait or a mainline with several branchlines with baited hooks, which can be reeled in manually or mechanically. A jig is a type of grapnel (or grappling hook), which is attached to a fishing line. Jigging involves manually or mechanically moving the jig in the water to lure prey, and then quickly pulling or jerking the fishing line to hook fish. Jigging for squid is usually done at night with lights to entice them closer to the surface. These hand-held fishing methods are considered environmentally responsible because there’s virtually no catch of unwanted marine life or habitat impacts.
Harpoons are poles that have a steel point with one or more barbs at the end and usually a retrieving line. When a fisherman targets a fish, he thrusts or shoots the harpoon into the animal and hauls it aboard. This traditional fishing method is still used today by skilled anglers to catch pelagic predators such as bluefin tuna and swordfish. Modern harpoons are shot by guns. Bycatch of unwanted marine life is not a concern because the species and size of the fish are identified before it’s caught.
Longlines have a central line, ranging anywhere from about a mile to 30 miles long, that’s strung with evenly spaced smaller lines with baited hooks. Drifting longlines are used near the surface to catch pelagic fish like tuna and swordfish, and set longlines are laid on or near the seafloor to catch bottom-dwellers like cod and halibut. A variety of species, including endangered sea turtles, seabirds, marine mammals and sharks, are also attracted to the bait. The accidental capture of some of these ocean animals can be reduced by setting drifting longlines deeper to allow many animals to swim over the top and adding streamers above the water to scare away seabirds. Also, a specially designed fishing hook called a circle hook can make it easier to release an animal that’s been accidentally caught.
Midwater trawls are cone-shaped nets that are pulled along in the midwater zone to catch species such as krill, rockfish and smelt. Two boats or otter boards maintain the net’s horizontal opening, and floats and/or weights support its suspension. Midwater trawlers vary in size, ranging from small ships to large industrial vessels that pull gigantic nets spanning the size of five football fields that are capable of catching an entire school of fish. This gear doesn’t contact the seafloor when it’s used in the midwater zone, but the catch of at-risk species occurs in many fisheries. Using streamer lines to scare away seabirds and avoiding areas with an abundance of marine mammals can reduce the amount of bycatch in these fisheries.
Pole-and-lines are poles with a single line, hook and bait that are used to catch a variety of fish ranging from open-ocean swimmers like tuna to bottom-dwellers like cod. They can be hand-operated or mechanized when operating in deep waters. Pole-and-line gears have very low catch of unwanted marine life because fishermen catch one fish at a time and they can release unwanted species.
Pots are cages or baskets that hold species such as lobsters, crabs and Pacific cod alive until fishermen return to haul in the catch. Pots have one or more openings and are used with or without bait. The second opening allows fish or species that are below the legal catch size to escape. They’re usually placed on the seafloor, but some are designed to be in midwater. While unwanted species can be released alive and habitat impacts tend to be minimal, the entanglement of whales and other species is a serious conservation concern in some pot fisheries. Also, ghost fishing occurs when lost or abandoned pots continue to capture fish.
Purse seines use a large wall of netting to encircle schools of fish. Fishermen pull the bottom of the netting closed—like a drawstring purse—to herd fish into the center. This method is used to catch schooling fish, such as sardines, or species that gather to spawn, such as squid. Floating object purse seines use natural or artificial fish aggregating devices, or FADs, to attract schools of tuna. Dolphin set purse seine vessels seek out the dolphins that are associated with the tuna species they’re targeting. Unassociated purse seines, also known as "free school" purse seines, target tuna schools without using either of these methods to aggregate the catch. When purse seiners use FADs, the accidental catch of juvenile fish, sharks and other vulnerable marine life can be a serious conservation concern. These impacts can be reduced by decreasing FAD use, using biodegradable or non-entangling FADs and improving management and data collection.
Trolling lines catch species such as salmon, mahi mahi and albacore tuna by luring them with moving fishing lines baited with hooks. Several trolling lines are often towed at the same time, and outriggers keep the lines away from the vessel’s wake. The lines can be hauled in by hand or mechanically. This fishing method has low catch of unwanted marine life because fishermen can quickly release unwanted species since the lines are reeled in soon after a fish takes the bait.
Fish Farming (Aquaculture)
In the next decade, the majority of fish we eat will be farm-raised, not wild. Global aquaculture includes over 100 species, farmed in everything from traditional earthen ponds to high-tech tank systems. Each farming system has its own distinct environmental footprint. By choosing seafood from better farms and production systems, consumers can play a positive role in reducing aquaculture's potential negative impacts.
In bag-and-rack shellfish culture, juveniles are cultivated in bags on racks above the seabeds. The juveniles (or spat) come from hatcheries, so wild populations aren't depleted and habitats aren't damaged by dredging for starter organisms. Since most cultivated shellfish filter-feed, there's no addition of wild fish feed, and therefore no impact on wild fish stocks. While nonnative species may be grown in these systems and can possibly escape—typically due to the contained shellfish spawning—overall, this is an environmentally responsible method of aquaculture.
Hatchery fish are bred and reared in nurseries, either for use in aquaculture or to be released and caught in wild-capture fisheries. When released in large numbers, hatchery-raised fish can compete with wild populations for food. There are also concerns about genetically weaker hatchery fish interbreeding with and threatening the viability of wild populations.
Open Net Pens or Cages
Open net pens or cages enclose fish such as salmon in offshore coastal areas or in freshwater lakes. Net pens are considered a high-impact aquaculture method because waste from the fish passes freely into the surrounding environment, polluting wild habitat. Farmed fish can also escape and compete with wild fish for natural resources or interbreed with wild fish of the same species, compromising the wild population. Diseases and parasites can also spread to wild fish living near or swimming past net pens.
Ponds enclose fish in a coastal or inland body of fresh or salt water. Shrimp, catfish and tilapia are commonly raised in this manner. Wastewater can be contained and treated. However, the discharge of untreated wastewater from the ponds can pollute the surrounding environment and contaminate groundwater. Moreover, the construction of shrimp ponds in mangrove forests has destroyed more than 3.7 million acres of coastal habitat important to fish, birds and humans.
Raceways allow farmers to divert water from a waterway, like a stream or well, so that it flows through channels containing fish. In the U.S., farmers use raceways to raise rainbow trout. If untreated, wastewater from the raceways can contaminate waterways and spread disease. Many governments require strict regulation and monitoring of water quality; by treating wastewater these risks can be greatly minimized. Escaped fish are another potential problem—they can compete with wild fish for natural resources and also interbreed with wild fish of the same species, potentially weakening the species genetically.
Recirculating systems raise fish in tanks in which water is treated and recycled through the system. Almost any finfish species such as striped bass, salmon and sturgeon can be raised in recirculating systems. Recirculating systems address many environmental concerns associated with fish farming—fish cannot escape, and wastewater is treated—but they are costly to operate and rely on electricity or other power sources.
Shellfish culture means that farmers grow shellfish on beaches or suspend them in water by ropes, plastic trays or mesh bags. The shellfish farmed using these methods—oysters, mussels and clams—are filter feeders and require only clean water to thrive. Filter feeders can actually filter excess nutrients out of the water, but farming shellfish in high densities in areas with little current or tidal flow can lead to the accumulation of waste. Also, historically, some shellfish culture has been responsible for the introduction of exotic species that can sometimes out-compete native species for natural resources.
Submersible Net Pens
Submersible net pens (or cages) are designed for use in offshore aquaculture and can be used for a variety of fish species. This method can be damaging to the local environment because water flows freely through the cages, carrying fish waste, uneaten food and chemicals into the surrounding water. Also, since the pens are open, there's the potential for farm diseases to transfer to wild fish populations.
Shellfish culture can be very sustainable. Species such as oysters, mussels and clams are filter feeders that don't require additional feed and therefore don't impact wild fish stocks. Farmers grow shellfish on beaches or suspend them in water by ropes, nets, trays or mesh bags. Habitat damage and impacts from effluent are generally minimal.
Ranching is the process of capturing valuable juvenile species, usually carnivorous top predators, then growing them to harvest size on farms. Highly profitable species such as bluefin tuna are caught at a relatively large size and "fattened" before harvest. In addition to concerns about the high use of feed and waste from such farming operations, ranched species can't contribute to their natural ecosystems, threatening the overall health of those environments.