Seafood Harvest Methods

Ocean Wise Recommendations with harvest method specified as “All Production Methods” denotes the recommendation covers all possible aquaculture production methods.

Bottom culture is a method of aquaculture in which shellfish and seaweeds are grown on the seabed. Shellfish are typically transferred from hatcheries and seeded onto the seabed to grow-out. Mature seaweeds and shellfish are later harvested by hand, rakes, or dredging.

Species typically harvested: Oysters, scallops, clams, and seaweeds

See Bottom Culture. In enclosed bottom culture organisms are confined inside or under nets or other containment structures set on the seafloor.

See Bottom Culture. In open bottom culture organisms are not confined under or within a containment structures and instead are grown in the open on the seafloor.

Diving comprises of gathering fish or invertebrates by hand or with simple hand implements with or without SCUBA equipment.

Species typically harvested: Sea urchins, sea cucumbers and geoduck clams

See Dredges and Hand implements. Hand dredges are small, light, handheld dredges consisting of a mouth frame attached to a holding bag constructed of metal rings or meshes. 

See Dredges. Mechanized dredges are gear that were specifically developed to dig and wash out organisms that have buried in the seabed while harvesting machines extract organisms from the water by forced sifting or pumping.

See Dredges. There are two main types of towed dredges, those that scrape the surface of the bottom and those that penetrate the sea bottom to a depth of 30 cm or more to harvest marine organisms. 

These harvest methods can cause significant damage to sensitive habitats and, as it is an unselective gear type can result in high bycatch. Limiting the area in which dredges are used and targeting sandy, rather than hard bottoms can help to minimize their impact.

Species typically harvested: Shellfish (e.g. scallops, mussels, and oysters)

Animated Seafood Watch video of a dredge (Credit: Seafood Watch)

See Falling Gear. Cast nets are composed of a circular, cone-shaped net with weights attached at regular intervals around the net’s perimeter. When thrown (“cast”) the net falls through the water and the weights at the net’s edge cause it to close, capturing any organisms inside. The gear is then retrieved through use of an attached line. Casting can occur from shore or small boat within shallow waters.

See Gillnets and Entangling Nets. Drifting gillnets consist of a single gillnet panel, or string of panels held open by floats on the upper line (head rope) and sometimes use of weights on the lower line (ground rope). The nets are marked by buoys and left to drift with the current either at the surface or at depth within the water column.

See Gillnets and Entangling Nets: Encircling gillnets are gillnets which are set vertically in shallow waters in such a way that they encircle fish. Once fish have been encircled by the net, noise or other means are used to force the fish to entangle in the netting.

Gillnets are walls of netting that are nearly invisible to the fish. Individuals who attempt to pass through the net become entangled by their gills. Gillnets can be set in a variety of configurations depending on the use of floats and weights used to suspend the netting. They can be set on stakes in shallow water, pinned to the seafloor with weights to catch demersal (bottom dwelling) species, or drift in the water column.

Gillnets can incur bycatch through the accidental capture of vulnerable animals including marine mammals, sea turtles, and sharks. However, these impacts can be reduced through a number of measures such as setting nets deeper in the water column to allow animals to swim over the top, or modifications to the gear such as the addition of pingers that warn passing marine mammals.

Species typically harvested: Salmon, cod, perch, trout, and sardines

Animated Seafood Watch video of a gillnet (Credit: Seafood Watch)

See Gillnets and Entangling Nets. Gillnets or entangling nets that are either anchored to the bottom or fixed, stretched between two or more stakes that are driven into the bottom within intertidal or freshwater habitats.

Targeted species: e.g., Salmon

Hand harvesting refers to the manual extraction of fish, invertebrate, and plant species. Hand harvesting is a selective method of fishing/farming as humans visually identify the species before harvest. This avoids the extraction of non-targeted species, and minimizes habitat damage.

Species typically harvested: Clams, barnacles, lobsters and sea urchins

Harpoons are long poles with a pointed, barbed, steel tip often attached to a retrieving line. Fishers target a specific fish and then throw or shoot the harpoon into the animal. Harpoons are highly selective gear that have near zero bycatch because the fisher identifies a fish based on species and size before catching it.

Species typically harvested: Bluefin tuna and swordfish

See Hooks and Lines. Buoy gear was developed as a fishing technique that would reduce high bycatch levels within swordfish fisheries. It is composed of a free-floating buoy attached to a fishing line containing one to several baited hooks. Buoys are set in straight lines and actively monitored by fishers. When a fish strikes a baited hook it pulls the buoy out of line which signals to fishers that a fish is hooked.

Species typically targeted: Swordfish

See Hooks and Lines and Longlines. Demersal, also known as deep-set, or set longlines are a method of longlining where fishing occurs near or on the seafloor. They can range in length from a few hundred meters in some coastal fisheries to over 50km in length in some large scale fisheries. Deep-set longlines do not have the same bycatch considerations as surface longlining.

See Hooks and Lines. Hand operated handlines are a type of hook and line fishing gear where a single hook and attached line are operated without an pole or rod.

Targeted species: Numerous finfish species

See Hooks and Lines. Handlines and pole and lines are a type of hook and line fishing gear where a single hook and attached line (either with or without an associated pole or rod) are operated by human or mechanically powered reels or drums.

Targeted species: Numerous finfish species

See Hooks and Lines. Hand operated handlines and pole and lines are a type of hook and line fishing gear where a single hook and attached line (either with or without an associated pole or rod) are operated by human powered reels or drums.

Targeted species: Numerous finfish species

See Hooks and Lines. Mechanized handlines and pole and lines are a type of hook and line fishing gear where a single hook and attached line (either with or without an associated pole or rod) are operated by mechanically powered reels or drums.

Targeted species: Tuna

See Hooks and Lines. A jig is composed of a baited or lured hook attached to a single line. The hook and line are jerked through the water in a manner that resembles a moving fish. When jigging for squid, fishing usually occurs at night and lights are used to attract the squid.

Targeted species: Finfish, squids

Longlines are composed of a mainline supported with floats or weights, and evenly spaced branch lines containing one to several baited hooks. Longlines supported by floats are known as drifting longlines and are commonly used to catch pelagic species like tuna and swordfish. Longlines can also be weighted and pinned to the seafloor to catch demersal (bottom dwelling) species like cod and halibut.

Longlines are an unselective fishing method and as such can have large impacts on other species which are accidentally caught as bycatch (e.g. birds, juvenile fish, marine mammals, and sharks). Longline gear can be modified to minimize these impacts through use of specially designed fishing hooks called circle hooks or the use of streamers above the water to deter seabirds.

Animated Seafood Watch Video of a longline (Credit: Seafood Watch)

See Hooks and Lines. Trolling is a hook and line fishing method that utilizes several fishing lines with baited hooks which are towed through the water by a vessel. The movement of these lines lures fish which are landed by hand or mechanically using small winches.

Species typically targeted: Tuna and salmon

See Hooks and Lines. Trotlines are a type of hook and line composed of a setline and multiple hooks (from six to several hundred).  Hooks are set at intervals from the mainline through attachment to short individual line segments called “trots” or dropper lines.

See Hooks and Lines. Vertical lines are a type of hook and line fishing composed of a fishing line attached to a weight and one or several hooks. The additional hooks are fixed to the mainline at short intervals with branch lines of a certain length.

See Lift Nets. Portable lift nets are hand operated, small nets composed of a horizontal netting panel or upward facing bag often supported by a rigid frame. They are are operated by submerging the net in the water column to the a desired depth and then by lifting the net from the water once targeted organism is identified above the netting.

A fishwheel is a waterwheel shaped device that is used in rivers to catch fish like salmon. Large paddles are rotated by the flowing water causing the fish wheel to rotate. Baskets associated with the paddles capture fish moving through the water, and through the rotation of the wheel deposits them within a holding tank.

Targeted species: Salmon and trout

Scoopnets and dipnets are composed of a net bag held open by a frame. They are small, hand-operated fishing gear used to scoop fish out of the water and commonly used in artisanal fisheries.

Net pens and cages are structures that contain farmed fish within open water. They can be composed of wood, net screens, or mesh which allows water to move freely into and out of the enclosure. Net pens can be enclosed only on the bottom and sides and float at the surface of the water column or be enclosed on all sides and submerged within the water column.

Net pens and cages can be problematic because the farmed species are in direct contact with the surrounding ecosystem. Waste water can affect the benthic habitat directly below the farms, and there is the risk that if farmed fish develop diseases and parasites, these can be passed on to wild populations. If any farmed fish escape from the pen, they can negatively affect wild populations by competing with them for food and habitat. Hybridization with wild individuals is also a concern, since this could produce genetically less fit offspring and compromise the quality of the wild population. If antibiotics are used in the net pens, their open nature and direct contact with the environment makes the potential for spread of antibiotic resistance in humans a serious concern.

Species typically harvested: Salmon and trout

Off-bottom aquaculture utilizes floating rafts, bags, or suspended ropes to grow shellfish. This system makes no contact with the seafloor, and shellfish are harvested with little to no bycatch. Since shellfish are filter feeders, they offer ecosystem benefits by reducing nutrient load in the water and do not require any external feed as they extract nutrition from plankton in the seawater. This means that shellfish farming puts no pressure on wild fish stocks for feed.

Species typically harvested: Oysters, mussels, clams, and scallops

See Off-Bottom Culture. Rope or frame aquaculture also called longline culture is a type of open-water off-bottom culture where cultured species are grown on ropes or diverse containers (e.g. baskets, stacked trays, lantern nets) suspended from anchored and buoyed surface or subsurface ropes (longlines).

Commonly culture species: Bivalve molluscs (e.g. mussels, oysters, scallops) and seaweeds (e.g. kelp). 

Ponds can be naturally occuring or man made and are relatively shallow and small bodies of fresh or saltwater used to grow fish and shellfish. This aquaculture method can vary from low-tech extensive ponds to highly sophisticated systems. Historically, aquaculture ponds have been built along coastlines, which has contributed to the destruction of mangrove forests, critical habitat for many species. Ponds can have significant impacts on the surrounding environment depending on the level of treatment water receives before it is discharged, and if farm-raised species are able to escape.

Species typically harvested: tiger shrimp, catfish and tilapia

Animated Seafood Watch Video of a Pond (Credit: Seafood Watch)

See Ponds. Extensive ponds are usually relatively small and shallow bodies of still water. They are characterized by their scale of production (yielding no more than 500 kg/ha/yr) and low production efficiency, use of natural waterbodies (e.g. lagoons, bays, embayments) and water fertilisation for nutrient provision, low initial costs and low level use of technology, and high dependence on local climate and water quality.

See Ponds. Intensive  ponds are usually relatively small and shallow bodies of still water. They are characterized by their scale of production (up to 200 tonnes/ha/yr), production efficiency, use of man made culture systems, high initial costs and high level use of technology, and tendency towards increased independence of local climate and water quality.

See Ponds. Semi-extensive ponds are usually relatively small and shallow bodies of still water. They are characterized by their scale of production (0.5—5 tonnes/ha/yr), use of supplemental feed, fertilizer use, stocking with wild-caught or hatchery-reared fry, the use of rainwater or tidal flow for water supply, and the presence of water exchange with the surrounding habitat.

See Ponds. Semi-intensive ponds are usually relatively small and shallow bodies of still water. Aeration may be used to maintain water quality. Production within semi-intensive ponds requires more on the use of external sources of feed  (homemade, commercially formulated, or use of water fertilization) than semi-extensive but less so than intensive systems. These facilities also rely on hatchery-raised stock for production. 

Raceways are long straight channels used to contain farmed fish. Raceways can either be flow-through, where water is diverted from a natural water body and is pumped out of the facility either treated or untreated. If untreated, wastewater can contaminate waterways and spread disease. Raceways can also recirculate water, meaning water is treated and re-used.

Species typically harvested: Rainbow trout

See Raceways. Indoor flow-through Raceways are indoor containment structures utilized in the cultivation of organisms for aquaculture. They are usually located above ground, with a long linear configuration, and have high rate of water turnover.  Water flows through each tank and the wastewater, which may contain nutrients, wastes, and/or chemicals leaves the facility, potentially impacting local wildlife and habitats. 

See Raceways. Outdoor flow-through Raceways are outdoor containment structures utilized in the cultivation of organisms for aquaculture. They are usually located above ground, with a long linear configuration, and have high rate of water turnover.  Water flows through each tank and the wastewater, which may contain nutrients, wastes, and/or chemicals leaves the facility, potentially impacting local wildlife and habitats. 

Recirculating aquaculture systems (RAS) are land based facilities that utilize tanks and a continuous flow of water to farm fish and shellfish. These facilities are somewhat unique because they use filtration systems to remove solid and particulate waste from wastewater allowing it to be reused and recirculated throughout the farm. This farming method addresses many of the environmental concerns associated with aquaculture. The filters used in RAS also highly limit the use of antibiotics and because RAS facilities clean and re-uses water, there are minimal impacts of wastewater on the surrounding environment. The land-based nature of these facilities also greatly limits the potential for disease and parasite transfer to the surrounding environment and the risk of escapes.

Species typically harvested: Rainbow trout, Arctic char, sturgeon, salmon

Animated Seafood Watch Video of a Recirculating System (Credit: Seafood Watch)

Silvoculture is a sustainable alternative to traditional shrimp ponds. Shrimp are raised within the mangrove forest, and farmers are often required to maintain a certain minimum cover of mangroves. No external feed is given to the shrimp, as they feed off the natural forest resources. Chemicals are not used, and disease is controlled by not overcrowding the shrimp.

Species typically harvested: Black tiger shrimp, whiteleg shrimp

Check out this video to see silvoculture in action.

Suripera is an artisanal fishing technique utilize by fishers in Mexico to capture shrimp. The method employs wind and tide driven skiffs to set nets and land catch.

See Seine Nets. Beach seines are long nets operated from shorelines primarily by hand. The seine net has floats attached to its top side and is weighted at the bottom. This net structure keeps the net in contact with the bottom, trapping fish within the area it encloses. Since schooling or spawning fish are easily targeted by beach seines, the use of beach seines must be well-regulated in order to be sustainable.

Species typically harvested: Sardines, salmon, mullet, and pompano

Danish seines (also known as anchor seine) is a variation on tradition seining techniques. The seine net is composed of a cone-shaped net with two long wings each attached to a fishing line and anchor.

Deployment of a danish seine occurs much like a hitter running the bases of a baseball diamond. At home plate an anchor and fishing line are deployed. The vessel then streams a straight course to first base, all the while extending the rope into the water. It then adjusts course and aims for second base, once there the vessel “shoots” the seine net, deploying it. The vessel then traces the other half of the diamond back to home plate, returning to the anchor. The net is then hauled, herding the fish into the net’s path and capturing the fish inside.

Pair seining is when two vessels work together to set and haul a single net.

Purse seines are nets that are deployed by boat to encircle a school of fish. Once set, fishers pull the bottom of the netting like a drawstring purse, to corral fish into the center of the net which is then hauled. Depending on the species targeted, purse seines can cause varying amounts of bycatch.

Purse seines can either be unassociated (also known as “free school”) or utilize fish aggregating devices (FADs).  To learn more, click the tabs below.

Species typically targeted: Tunas, mackerel, herring, sardines, anchovies, and salmon

See Surrounding Nets: Purse Seines. Purse seines can either be unassociated (also known as “free school”) or utilize fish aggregating devices (FADs).  FADs consist of floating material which serve to attract open-ocean fish.  This method can result in high bycatch of threatened species including sharks, juvenile tunas and turtles.

Species typically targeted: Tunas, mackerel, herring, sardines, anchovies, and salmon

See Surrounding Nets: Purse Seines. Unassociated purse seines or “free school” purse seines, target schooling fish without using fish aggregating devices (FADs). Floating object purse seines are purse seine nets deployed with a fish aggregating device (FAD). FADs consist of floating material which serve to attract open-ocean fish.  This method can result in high bycatch of threatened species including sharks, juvenile tunas and turtles.

Species typically targeted: Tunas, mackerel, herring, sardines, anchovies, salmon

See Surrounding Nets: Purse Seines. Historical, dolphin pods have been used as a natural cue to aid harvestors toward areas of abundant schooling fish (called “setting on dolphins”). Once the netting has been set, encircled marine mammals cannot escape and can become entangled, injured, or stressed. When you see dolphin safe tuna, it implies that this strategy was not used.​

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Seine nets are a classification of surrounding nets that utilize a vertical panel of netting called a seine which is held open by floats on the upper panel and weights on the lower panel. Seine nets can be utilized in a variety of ways including from shore (beach seines) or in deep water (e.g., purse seines).

See Tanks. Indoor flow-through tanks are indoor containment structures utilized in the cultivation of organisms for aquaculture. They are usually located above ground and have high rate of water turnover.  Water flows through each tank and the wastewater, which may contain nutrients, wastes, and/or chemicals leaves the facility, potentially impacting local wildlife and habitats. 

See Tanks. Outdoor flow-through tanks are outdoor containment structures utilized in the cultivation of organisms for aquaculture. They are usually located above ground and have high rate of water turnover.  Water flows through each tank and the wastewater, which may contain nutrients, wastes, and/or chemicals leaves the facility, potentially impacting local wildlife and habitats. 

Traps are a classification of fishing gear that includes pots, traps, trapnets and more. All traps are immobile enclosures composed of metal or flexible nets placed on the seafloor or lake or river bottom.

Traps can utilize escape hatches and other technologies that allow undersized or immature individuals to escape. Additionally, bycatch accidentally caught can often be released live and uninjured.

Traps are generally a sustainable way of fishing, unless they are placed in areas where the main fishing line which ties them together has the potential to entangle migrating marine mammals, or if they are placed on top of sensitive habitat.

See Traps. Crab rings are a type of trap that are specifically designed to catch crabs. Essentially a collapsible basket on a rope, crab rings lay flat, collapsed on the seafloor. When the rope is pulled, the basket take shape and traps any crabs attracted to the bait placed within the basket.

See Traps. Pots are cages or baskets which can be made from a variety of materials including wood, metal, or plastic. They may have one or more entrance are are designed to attract organisms to enter (sometimes through use of bait) but make it extremely difficult or impossible for them to escape.

Pots are commonly set in rows or “strings” on the seafloor. The gear is then left to “soak” for a period of hours to days before being hauled to the surface.

Target species: e.g., Crabs, lobsters, shrimp, sablefish

Animated Seafood Watch video of traps/pots (Credit: Seafood Watch)

See Traps. Pond nets, stow nets, and trapnets consist of cylindrical or cone-shaped bags of netting, or netting panels mounted on rings or held in place with stakes. They utilize leaders of netting to guide fish into the net bag.

Species typically targeted: Eels, salmon 

Trawls are cone-shaped nets that are towed by a boat through the water column (pelagic / midwater trawls) or against the seafloor (bottom / demersal trawls). Depending on type, a trawl net can be held open horizontally by beams, large rectangular otter boards, or by the distance between two vessels. Trawl nets are held open vertically through the use of floats or weights. 

Trawl nets vary in length however industrial scale trawlers can be immense. Trawls are an efficient but unselective fishing method which can incidentally capture a variety of species including some of conservation concern (e.g., marine turtles) as the net will capture any organism it encounters that is large enough not to pass through the mesh. New technologies like turtle excluder devices and strong management can reduce bycatch and make trawling more sustainable.

You can learn more about the diverse gear types that make up the trawls classification by clicking the tabs below.

See Trawls and Bottom Trawls.  Beam trawls are a trawling method where the net is held open by a large horizontal beam which can range in size up to 12m.

See Trawls and Bottom Trawls. Flyshooter trawling (also known as Scottish seine) is a variation on tradition trawling techniques. The trawl net is composed of a cone-shaped net with two long wings each attached to a fishing line and buoy.

Deployment of a flyshooter trawl occurs much like a hitter running the bases of a baseball diamond. At home plate the first buoy and flyshooter rope are thrown into the water. The vessel then streams a course to one side of where the fish were seen (first base), while deploying the rope. It then adjusts course and aims for where the fish school was seen (second base), once there the vessel “shoots” the seine net, deploying it. The vessel then traces the other half of the diamond back to home plate, returning to the first buoy. The net is then hauled, herding the fish into the net’s path and finally closed, capturing the fish inside.

See Trawls and Bottom Trawls. Nephrops trawls are bottom trawls that are specifically designed to catch nephrops lobster.

When used over certain types of bottom habitat, trawls can cause destruction of physical structures such as corals and sea sponges. Impacts of bottom trawls can be minimized by modifying the nets and implementing management measures that limit designated areas that can be trawled.

Species typically harvested: Cod, halibut, sole, lobster, and rockfish

Animated Seafood Watch video of a bottom trawl (Credit: Seafood Watch)

To learn more about these gears please view the Bottom / Demersal Trawls or Twin Rig Trawls tabs.

See Trawls and Bottom Trawls. Otter trawls use two large otter boards to keep the mouth of the trawl net open.

When used over certain types of bottom habitat, trawls can cause destruction of physical structures such as corals and sea sponges. Impacts of bottom trawls can be minimized by modifying the nets and implementing management measures that limit designated areas that can be trawled.

Species typically harvested: Cod, halibut, sole, lobster, and rockfish

Animated Seafood Watch video of a bottom trawl (Credit: Seafood Watch)

See Trawls and Bottom Trawls. Rockhopper trawls are used to fish for organisms on rocky seafloor habitats and employ large bobbins that are designed to lift the trawl net away from the seafloor when it encounters an obstacle.

When used over certain types of bottom habitat, bottom trawls can cause destruction of physical structures such as corals and sea sponges. Impacts of bottom trawls can be minimized by modifying the nets and implementing management measures that limit designated areas that can be trawled.

Species typically harvested: Cod, halibut, sole, lobster, and rockfish

Animated Seafood Watch video of a bottom trawl (Credit: Seafood Watch)

See Trawls and Bottom Trawls. A skimmer trawl consists of a fishing net fixed to a large L shaped frame. The nets and frames are suspended from large booms which extend from the sides of the vessel an allow the nets to be pushed through shallow, nearshore waters. Skimmer trawls are used with chained footropes an a tickler chain that stir up the seafloor and lift bottom dwelling organisms into the water column where they are trapped in the net.

When used over certain types of bottom habitat, these trawls can cause destruction of physical structures such as corals and sea sponges. Impacts of bottom trawls can be minimized by modifying the nets and implementing management measures that limit designated areas that can be trawled.

Species typically harvested: Shrimp

See Trawls. Bottom trawls use weighted nets and rollers to harvest organisms that live on or near the seafloor.

When used over certain types of bottom habitat, bottom trawls can cause destruction of physical structures such as corals and sea sponges. Impacts of bottom trawls can be minimized by modifying the nets and implementing management measures that limit designated areas that can be trawled.

Species typically harvested: Cod, halibut, sole, lobster, and rockfish

Animated Seafood Watch video of a bottom trawl (Credit: Seafood Watch)

See Trawls. Midwater trawls are towed at a variety of depths within the water column but do not contact the ocean floor. This harvest method is used to target pelagic (open water dwelling) species.

Species typically targeted: Shrimp and schooling fish (e.g., anchovies)

Animated Seafood Watch video of a mid-water trawl (Credit: Seafood Watch)

See Trawls. Pair trawling is a fishing technique where two vessels work together to tow a single trawl net either through the water column or against the sea floor.

Species targeted: Finfish and invertebrates

See Trawls. Shrimp trawls are designed specifically to catch different species of shrimp.

Species targeted: Shrimp

See Trawls. Twin rig trawling is a fishing technique where a single vessel tows two small trawl nets side by side.

Species targeted: Finfish and invertebrates