The environmental impact of different fishing and farming methods vary — choosing less damaging methods supports a healthy ocean.
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
Seine nets encircle and herd fish with a long wall of netting. Long wings and ropes are used to operate the gear, and the net may have a smaller mesh bag called a codend, which retains the catch. When in use, beach seines are hauled to shore by hand or other machinery, and boat seines are towed by one or two vessels. The catch of unwanted species can be a conservation concern in these fisheries. Seine nets are used to catch cod, haddock, hake, pollock, salmon, snapper, and many other species.
Bottom trawls
Bottom trawls are cone-shaped nets that are pulled along the seafloor to catch cod, halibut, lobster, rockfish, shrimp and other bottom-dwellers. These fishing gears are configured to stay open in different ways. Often floating headropes and weighted footropes hold the nets open vertically, and beams, otter boards, or two boats keep them open horizontally. The variety and amount of bycatch in many bottom trawl fisheries is a pervasive problem, and the heavy gear can damage sensitive habitats. Reducing these harmful effects requires limiting when and where trawling can occur and gear modifications that allow unwanted marine life to escape and lessen impacts on the seafloor.
Buoy gears
Buoy gear consists of a bite indicator and a float supporting a mainline with hooks set at a minimum depth of 90 meters — placing the hooks below a layer of water in the ocean known as the Thermocline. Most marine life thrives in the warm, oxygen-rich water above this layer, however, other species like swordfish can dive to the cold water beneath it. This fishing method allows for more selective fishing and significantly reduces the unintentional capture of non-target species. When incidental catches of non-target species do occur, the animals are often released alive as a result of the bite indicator promptly alerting fishers of a catch. In turn, when a swordfish is caught using buoy gear, the meat is fresh and provides fishers with a higher quality product and monetary return.
Dredges
Dredges are metal, cage-like gears that are dragged over the seafloor to dig out clams, oysters, scallops, and other species. These fishing gears may or may not have components – such as rakes, teeth, or hydraulic jets – which dislodge and flush out animals. Types include hand dredges, towed dredges, and mechanized dredges. Dredges can have significant impacts on sensitive seafloor habitats and bottom-dwelling species. One way to reduce these harmful effects is to limit the areas where dredging can occur.
Gillnets
Gillnets are walls of stationary or drifting netting. When fish swim into the netting, they become entangled or entrapped. These fishing gears are used on or near the seafloor, in midwater, or near the surface. In some gillnet fisheries, vulnerable ocean animals like sea turtles, marine mammals, and sharks can be caught. These impacts can be reduced by setting the netting deeper in the water column to allow animals to swim over and adding pingers to warn passing marine mammals. Gillnets are used to catch cod, perch, salmon, sardines, trout, and many other species.
Handlines and jigs
Handlines are used to catch high-value tuna and other species. This gear consists of a fishing line with a baited hook. When in use, fishermen haul in the line hand-over-hand. Jigs consist of a fishing line and grapnel with multiple hooks. When in use, jigs are manually or mechanically moved in the water to lure fish and then quickly pulled or jerked to hook them. Squid jigging is usually done at night with lights to entice them closer to the surface, but it can also be done during the day using underwater lights. These fishing methods are considered a more environmentally responsible because there's very little catch of unwanted marine life.
Illustration © Mathew Squillante
Harpoons
Harpoons are spear-like gears with a detachable sharp point (that has one or more barbs) attached to a retrieving line. When fishermen target a fish, they thrust or shoot the harpoon into the animal and haul it aboard. Modern harpoons are shot with guns. The catch of unwanted marine life isn't a concern because fishermen identify the species and size of the fish before it's caught. Harpoons are used to catch large pelagic predators, such as tuna and swordfish.
Longlines
Longlines have a mainline and evenly spaced branch lines with baited hooks. They can be many miles long and have hundreds or thousands of hooks. Set longlines are placed on or near the bottom. Drifting longlines are set near the surface and at different depths in the water column. Bycatch of at-risk or overexploited species can be a significant conservation concern in longline fisheries, but gear modifications can reduce impacts on other marine life. For example, sinking drifting longlines deeper allows many animals to swim over them, and adding streamers above the water scares away seabirds. Also, a specially designed fishing hook called a circle hook can make it easier to release turtles and other animals that have been accidentally caught. Longlines are used to catch cod, halibut, tuna, swordfish, and many other species.
Midwater trawls
Midwater trawls herd and sieve fish with a cone-shaped net. The nets are configured to stay open in different ways. Weights on the lower wings keep the net open vertically, and the horizontal opening is maintained by otter boards or two boats. When in use, fish are herded into the net as the gear is towed. 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. Midwater trawls are used to catch anchovies, cod, flounder, krill, pollock, rockfish, squid, and many other species.
Pole-and-lines
Pole-and-line gears catch fish with one or more fishing lines with baited hooks. They’re used to catch a variety of fish ranging from open-ocean swimmers like tuna to bottom-dwellers like cod. The lines may or may not be attached to poles, and reels are often used to operate and retrieve the catch. Depending on the type and where fishing occurs, the gears are mechanically- or hand-operated. Harmful impacts on other species tend to be minimal because fishermen can release unwanted marine life.
Pots
Pots are cage-like gears with one or more openings that animals can easily enter but are hard to exit. Pots are set with and without bait, and they may have an opening that allows undersized or non-targeted marine life to escape easily. Pots are usually placed on the bottom, 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. Many species are caught with pots, such as cod, crab, lobster, octopus, and shrimp.
Purse seines
Purse seines surround fish with a large wall of netting. Evenly spaced rings are attached to the lower edge of the net, and a purse line made of steel or rope runs through the rings. When in use, the net is closed like a drawstring purse to capture fish. Floating object purse seines use natural or artificial floating objects called fish aggregating devices (FADs) to lure schools of tuna. When FADs are used, the 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. Unassociated purse seines, also known as "free school" purse seines, target tuna without using FADs. Purse seines are used to catch many other species too, such as squid, pollock, salmon, and anchovies.
Trolling lines
Trolling lines catch fish with moving fishing lines with baited hooks. Several trolling lines are usually towed at the same time, and the lines are hauled in manually or mechanically. Fishermen can quickly release unwanted species because the lines are reeled in soon after fish take the bait. Trolling lines are used to catch flounder, octopus, salmon, swordfish, tuna, and many other species.
Farming methods
In the next decade, the majority of fish we eat will be farm-raised, not wild. Over 100 marine and freshwater species are farmed today using methods 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, you can play a positive role in reducing aquaculture's potential negative impacts.
Bottom culture
Bottom culture involves growing shellfish such as clams, mussels and oysters on the seabed. Types include enclosed bottom culture where the shellfish are inside or under a net or other containment structure. When shellfish are cultivated using open bottom culture, they’re not confined or covered in any way. After an appropriate growth period, the shellfish are harvested by hand, rakes or dredging. Seaweed may also be grown by bottom culture.
Off-bottom culture
Off-bottom culture involves growing shellfish such as clams, mussels and oysters in ways where they don’t touch the ocean floor. Types include bag culture where shellfish are grown in mesh bags on stands in the intertidal zone. Raft culture entails growing shellfish on old shells that have been punctured, strung together and attached to raft-like structures. Longline culture involves growing shellfish on ropes or inside containers that are suspended from anchored or buoyed ropes. Seaweed is also farmed using off-bottom culture. Overall, off-bottom culture methods have relatively few environmental impacts.
Pens
Pens are structures that hold farmed fish in open water as they grow. They’re made with wooden, mesh or net screens, which allow water to flow freely through them. Net pens can be in marine waters to farm species such as salmon and trout or freshwater to farm species such as tilapia and trout. Types include pens, which are fixed to the bottom in shallow waters. Net pens are enclosed on the bottom and sides. Submersible net pens are fully enclosed and submerged, usually in offshore marine waters.
Ponds
Ponds enclose fish and crustaceans in a relatively shallow and usually small body of freshwater or saltwater. They vary considerably from simple, low-tech extensive ponds to sophisticated hyper-intensive ponds where farmers have significant control over the rearing process and pond conditions and production per hectare is very high.
Historically, ponds were built along the coast and contributed to the destruction of mangrove forests. If water is discharged without treatment or screening, it can impact the surrounding environment or allow farm-raised species to escape. Closed systems, where water is treated and used for multiple production cycles, reduce the risk of escapes and pollution. Shrimp, catfish and tilapia are commonly raised in ponds.
Raceways
Raceways are long, linear containment structures used for farming fish. They’re often in a terraced configuration and usually above ground. These systems can be indoors or outdoors. Types include flowthrough where the wastewater leaves the facility and recirculating where the water is treated and re-used. Treating wastewater can greatly minimize environmental impacts, which can include contamination of waterways and spreading disease to wild fish. Species such as tilapia and rainbow trout are farmed in raceways.
Recirculating tanks
Recirculating tanks have continuous water flow, and the wastewater is treated and re-used. These systems can be indoor or outdoor, and they’re usually above ground. This farming method addresses many of the environmental concerns associated with aquaculture. The farms can be built in a variety of locations to avoid sensitive habitats. They can also minimize or avoid the discharge of pollutants beyond the farms. The potential for disease and parasite transfer to the natural environment is low, and escapes of farmed fish can be prevented. Many finfish species such as Arctic char, striped bass and sturgeon can be raised in land-based, recirculating tanks.
Extensive to intensive shrimp ponds
Most shrimp produced globally are farm-raised in ponds. As ponds are built or modified, inputs like fertilizers, aerators, and feed may be added. Farms range from extensive or low input to intensive or high input. Each step towards intensification works to increase the production of the pond beyond its natural capacity. No matter the method, risks are present when altering any landscape, making it important for farmers to use sustainable aquaculture practices so they can benefit from the surrounding environment while promoting the well being of the landscape.
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