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How Fish are Caught or Farmed
Fishing Methods
Commercial fisheries use a variety of fishing methods and fishing gear to catch the fish we eat. Some are environmentally friendly; others aren't. Click on a method for more information.
Fish farming, also known as aquaculture, uses a variety of methods to grow or breed fish or shellfish in marine or fresh water. Fish farms currently provide one-third of all seafood. However, this amount will increase in the future to help meet a growing global demand for seafood that can't be met by wild fisheries alone. Popular seafood such as salmon and shrimp are farm raised in addition to being fished in the wild. Other popular seafood items such as tilapia, catfish and mussels are almost always farm raised.
Fish farming can be done responsibly but not all fish farms are created equal. For example, it's best to farm fish that are omnivores (plant and protein eaters) rather than carnivores (protein eaters). Carnivores, like shrimp, salmon and tuna, require feed that's made from wild fish (either converted into pellets or processed as whole fish). Instead of alleviating pressures on wild fish, farming carnivorous fish actually creates a new demand that wild fisheries can't meet. Some fish, like tilapia, are vegetarian and thrive on inexpensive, vegetable-based foods. You can learn more about aquaculture in our "Aquaculture: Is Fish Farming the Answer?" section. Click on a fish farming technique for more information.
Fishermen drag a heavy frame with an attached mesh bag—called a dredge—along the seafloor to catch bottom-dwelling shellfish. Some dredges have metal “teeth” along the base of the frame that act like a rake. As the gear is dragged along the seafloor, it stirs up shellfish, which flow into the bag. Water, sand or mud pass through the mesh. The durable bag is made of metal rings to withstand being dragged along the seafloor.
Dredgers rake the seafloor for shellfish
Most dredgers catch scallops, clams, oysters and other shellfish that live on the seafloor or burrow into mud or sand.
Dredging damages the seafloor and results in unintentional catch
Dredges cause significant habitat damage when dragged along gravel and rocky bottoms. Dredges also smooth out sandy and muddy bottom habitats, removing or smothering a variety of animal and plant life.
Fish, sponges and other marine life unintentionally caught as bycatch are unlikely to survive under the weight of the heavy bag.
A gillnet is a curtain of netting that hangs in the water at various depths, suspended by a system of floats and weights, or anchors. The netting is almost invisible to fish as they swim into the gillnet. The mesh spaces are large enough for a fish's head to pass through, but not its body. As the fish tries to back out, its gills are entangled in the net.
The size of a gillnet's mesh determines the type of fish it will catch
Small mesh can catch small fish like sardines. Larger mesh can entangle fish such as salmon and cod, while allowing smaller species to pass through.
Gillnets may accidentally entangle and kill sea turtles
Gillnets entangle large numbers of marine mammals and sea turtles in addition to other marine life, resulting in a significant amount of bycatch.
Habitat damage can occur when gillnets anchored to the seafloor are hauled in and become tangled on structures such as coral and rocky bottoms.
Harpooning is a traditional method for catching large fish—and it’s still used today by skilled fishermen. When a harpooner spots a fish, he or she thrusts or shoots a long aluminum or wooden harpoon into the animal and hauls it aboard.
Harpooners fish for open ocean swimmers Harpooners catch large, pelagic predators such as bluefin tuna and swordfish.
Harpooning is an environmentally responsible fishing method Bycatch of unwanted marine life is not a concern because harpoon fishermen visually identify the species and size of the targeted fish before killing it.
Hook-and-line fishermen use a pole (rod) and fishing line with one to several hooks. Handliners don’t use a pole—they simply hold a line in their hand. To attract fish, hook and liners use artificial lures or bait, “jigging” or jerking the line to simulate the motion of smaller fish. Sometimes they toss baitfish into the water to start a feeding frenzy among the fish. The catch is hauled in manually or with a mechanized reel.
Hook and liners fish near the surface and down below Hook and liners target a variety of fish, ranging from open ocean swimmers, like tuna and mahi mahi, to bottom dwellers, like cod.
Hook and lining is an environmentally responsible fishing method Fishermen can quickly release unwanted catch from their hooks since lines are reeled in soon after a fish takes the bait.
Longliners attract fish with a central fishing line that ranges from one to more than 50 miles (80 km) long. This central line is strung with smaller lines of baited hooks, which dangle at spaced intervals. After leaving the line to “soak” for a time to attract fish, longliners return to haul in their catch.
Longlines at different depths attract different species Pelagic longliners hang their hooks near the sea surface to catch open ocean fish, such as tuna and swordfish. Demersal—or “bottom”—longliners float their hooks just off the seafloor to catch fish that live on or near the bottom, such as cod or halibut.
Pelagic longlining can accidentally kill sea turtles and seabirds
The baited hooks of pelagic longlines attract a variety of open ocean swimmers, such as endangered sea turtles, sharks and other fish, resulting in wasteful bycatch.
As the line is deployed into the water, seabirds dive for the bait and are ensnared on the hooks and drown.
By sinking their longlines deeper, U.S. fishermen avoid the migratory paths of sea turtles. Other innovations to reduce bycatch include the use of “circle” hooks to ease the release and survivability of unwanted species and the deployment of longlines through a chute to reduce seabird interactions.
A purse seine is a large wall of netting that encircles a school of fish. Fishermen pull the bottom of the netting closed (like a drawstring purse), herding the fish into the center. Purse seiners either haul the net aboard or bring it alongside the boat to scoop out the fish with smaller nets.
Purse seines are primarly used for schooling fish Fishermen use this method to catch schooling fish, such as sardines, or fish that gather to spawn, like squid. The most popular fish caught by purse seines are tuna used for canning.
Purse seining for tuna results in large amounts of unintended catch
To locate schools of tuna, fishermen look for schools of dolphins (tunas often travel below dolphins) or set out floating objects (logs or rafts) to attract fish in the open ocean.
The net encircles the school of tuna, but also catches the dolphins and a variety of other species, including sharks, sea turtles and juvenile fish.
In response to public outcry over the deaths of hundreds of thousands of dolphins, innovations have been developed to release dolphins alive—but dolphin populations have yet to recover. Scientists believe this may be due to the stress of the chase and frequent capture.
Traps and pots are submerged wire or wood cages that attract fish and hold them alive until fishermen return to haul in the gear. Traps and pots may or may not be baited, and they usually lie on the bottom—either singly or in a row. A rope runs from the trap or pot to a buoy floating at the surface, so fishermen can locate their gear.
Traps and pots catch bottom-dwellers Traps and pots are often used to catch lobsters, crabs and shrimp. They're also used to catch bottom-dwelling fish, such as sablefish or Pacific rockfish.
Most traps and pots are environmentally responsible, but have issues too
Baited traps may attract juveniles or unintended species. However, these animals can either escape through specially designed vents or be released alive once the trap is hauled aboard.
Traps may damage seafloor habitats when large ocean swells and tides bounce the gear around. Hauling in a row of traps may also drag the cages along the seafloor, causing damage.
Marine mammals can become entangled in the lines connecting the traps to the buoys.
Trawlers tow a cone-shaped net behind a boat. They tow midwater trawl nets at various depths, ranging from just below the surface to just off the seafloor. They drag bottom trawl nets along the seafloor. Trawlers can add chains to the mouth of a net to stir fish like shrimp and flounder up off the seafloor and into the net. They can also add heavy tires—called “rockhoppers”—to help the net roll over rough, rocky seafloor areas without getting snagged.
Trawling at different depths catches different animals Midwater trawlers catch faster-swimming schooling fish such as sardines. Bottom trawlers catch fish that live on or near the seafloor, such as cod, flounder and shrimp.
Trawl nets catch everything in their path and can damage the seafloor
Pelagic trawlers often accidentally catch endangered sea turtles, juvenile fish and other unwanted species, resulting in a significant amount of bycatch. Trawlers (such as U.S. shrimpers) can reduce bycatch by adding turtle excluder devices and bycatch reduction devices to their nets, which allow sea turtles and unwanted fish to escape.
Dragging nets along the seafloor can damage or destroy fish habitat. Bottom trawlers can minimize habitat damage by avoiding rocky or coral habitats and ceasing the use of rockhopper gear.
Trolling is a hook-and-line method that tows fishing lines behind or alongside a boat. Fishermen use a variety of lures and baits to “troll” for different fish at different depths.
Trollers catch fish that will follow a moving lure or bait Trollers catch fish that will follow a moving lure or bait, such as salmon, mahi mahi and albacore tuna.
Trolling is an environmentally responsible fishing method Fishermen can quickly release unwanted catch from their hooks since lines are reeled in soon after a fish takes the bait.
Ponds enclose fish in a coastal or inland body of fresh or salt water. Wastewater can be contained and treated. Shrimp, catfish and tilapia are some of the most common species raised in ponds.
What are the issues?
The construction of shrimp ponds in mangrove forests has destroyed more than 3.7 million acres (1.5 million hectacres) of coastal habitat important to fish, birds and humans.
The discharge of untreated wastewater from the ponds can pollute the surrounding environment and contaminate groundwater.
Farmers divert water from a waterway, like a stream or well, so that it flows through channels containing fish. Farmers usually treat the water before diverting it back into a natural waterway. The government requires strict regulation and monitoring of on-site and nearby water quality. In the U.S., farmers use raceways to raise rainbow trout.
What are the issues?
If untreated, wastewater from the raceways can contaminate waterways and spread diseases.
Farmed fish can potentially escape and compete with wild fish for natural resources. Escaped fish can also interbreed with wild fish of the same species, compromising the hardiness of the wild population.
Recirculating systems enclose fish in tanks, where water is treated and recirculated through the system. Almost any finfish species such as striped bass, salmon and sturgeon can be raised in recirculating systems.
What are the issues?
Recirculating systems address many environmental concerns associated with fish farming: fish cannot escape, and wastewater is treated.
However, recirculating systems are costly to operate and rely on electricity or other power sources.
Farmers grow shellfish on beaches or suspend them in water by ropes, plastic trays or mesh bags. The shellfish farmed using these methods are filter feeders and require only clean water to thrive. Oysters, mussels and clams are cultured using these methods.
What are the issues?
Since oysters, mussels and clams are filter feeders, they
can actually cleanse nutrient-rich water.
Farming shellfish in high densities in areas with little current or tidal flow can lead to the accumulation of waste.
Historically, shellfish culture has been responsible for the introduction of exotic species that can sometimes out-compete native species for natural resources.
