Seafood Harvest Methods

Fishing Methods: The type of fishing gear used to catch wild fish can determine whether a species is harvested sustainably or not. Fishing gear can cause non-target species to be caught accidentally as bycatch if they are unselective. They can also cause damage to the habitat if they touch or drag across the ocean floor.

Aquaculture Techniques: Humans eat more farmed seafood than wild, and farmed fish production surpassed wild capture fisheries in 2014. As farmed seafood becomes more and more prevalent in our diets, it is important that the seafood be raised sustainably so that the environment is impacted as little as possible. Just like there are sustainable and unsustainable methods of catching wild fish, there are also sustainable and unsustainable methods of farming fish.

Barriers, fences, weirs, corrals, and similar fishing methods utilize a variety of materials such as branches, stakes, netting, and rocks to obstruct fish movement. These harvest methods are employed in the marine intertidal zone or in rivers or streams. They can be used to capitalize on tidal action and trap marine fish in the intertidal as the tide recedes or can be used to direct fish movement to a particular location for capture.

Species typically harvested: Salmon, eel, perch, whitefish

Beach seines consist of a long net operated from shorelines by hand. The net is weighted at the bottom and has floats at the top. Fishers use the beach seine to encircle fish which are then brought onto shore. Since schooling or spawning fish are easily targeted by beach seines, the use of beach seines must be well-regulated in order to be used in a sustainable manner.

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

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

A bottom trawl consists of a large, cone shaped net that is dragged behind a moving fishing vessel. Unlike midwater trawls, bottom trawls are weighted, and utilize rollers to drag across the seafloor. 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)

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

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

In the equatorial Eastern Pacific Ocean, dolphins and tuna (mainly yellowfin but also skipjack) are known to associate and swim together, which is a behaviour unique to this part of the world. Since dolphins must surface to breathe, fishers often rely on spotting dolphins in order to find schools of tuna. Purse seine fleets exploit this behaviour by setting their nets these inter-species schools, which has resulted in the term “dolphin set”.

Dredges are large metal-framed baskets that are dragged across the ocean floor. They are equipped with large metal teeth that dig into the seabed to lift shellfish buried in the mud or sand. This harvest method 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)

Falling gear is a classification of fishing methods comprised of gear types that are designed to capture fish by falling and closing around them. This harvest method is typically used in shallow waters within artisanal fisheries. Some examples of falling gear include cast nets and cover or lantern pots.

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.

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. In contrast, unassociated purse seines or “free school” purse seines, target schooling fish without using FADs.

Species typically targeted: Tunas

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)

Greenstick gear was developed as a fishing technique that would reduce the high bycatch levels of tuna fisheries. With this fishing method, a moving vessel is equipped with a vertical pole (the “greenstick”) from which a main fishing line is deployed and kept straight using a float at its end. Up to 10 artificial lures are attached to the main line with individual lines and skip across the water in order to attract tunas. When a tuna is hooked, the individual line detaches from the main line and can be reeled in.

Like greenstick gear, buoy gear was also developed to reduce bycatch levels. This fishing gear targets swordfish. Buoy gear consists of several buoys from which one to two baited hooks are attached. Each buoy is equipped with a light, and the buoys are connected with a main line in a straight configuration. The gear is deployed at dusk. When a swordfish is hooked, it drags the buoy out of line which is visibly detected using the lights, and can be reeled in.

Species typically targeted: Tuna, swordfish

Credit: PEW Charitable Trusts

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

Hook and line fishing is a highly selective way of fishing. A fishing vessel pulls several fishing lines with flashing lures through the water column. This method is selective because only fast-moving fish can swim quickly enough to take the bait, and any non-target fish which is accidentally caught can be immediately returned to the ocean live. This fishing method does not make contact with the ocean floor and causes minimal amounts of habitat damage.

Species typically targeted: Tuna, salmon

Credit: Seafood Watch

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

Harvesting machines are used to extract fish or shellfish from the water by forced sifting or pumping.

Species typically harvest: Mussels and clams

Hooks and lines are a classification of fishing methods including many gear types (e.g. longlines, jigs, trolling lines, and trotlines). Hook and line fishing utilizes a fishing line (or lines) with one to several hooks to catch fish.

Species typically targeted: Swordfish, tuna, squid, salmon, mackerel, and rockfish

Lift nets are a classification of fishing method made up of several gear types. All lift nets are composed of a net bag or horizontal net panels used in combination with bait or light to attract fish and invertebrates. Lift nets are submerged and left within the water column for a set amount of time, then retrieved to capture attracted fish or invertebrates.

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)

Midwater trawls are cone-shaped nets that are pulled by a boat. The net is held open by two large boards attached to the net ends, or through pair trawling, when a net is pulled by two vessels.  Midwater trawls do not contact the ocean floor and are used to target pelagic (open water dwelling) species.

Species typically targeted: Warmwater shrimp, pelagic fish, and schooling fish (e.g. anchovies)

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

Miscellaneous gear encompasses a variety of fishing gear types that are not classified by the Food and Agriculture Organization of the United Nations. It includes harvest methods such as push nets, drive in nets, pumps, and the use of trained animals in the capture of aquatic species.

Net pens 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 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

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)

Traps are baited, immobile enclosures composed of metal or flexible nets placed on the seafloor or lake or river bottom. Marine traps typically target crustaceans, however they can also target bottom dwelling fish such as cod or sablefish. While freshwater traps capture crustacean or finfish species. Animals are able to enter the trap/pot through an opening of a specific size and shape, but are unable to leave. Traps and pots are selective as they are designed to catch specific species. The mesh size on the traps allow for undersized or immature individuals to escape. Additionally, any bycatch accidentally caught e.g. non-target species like octopus, undersized individuals, and females carrying eggs can be released live and uninjured. Traps and pots 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.

Species typically targeted: Crabs, lobsters and shrimp

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

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).  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

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

Scoopnets 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.

Seine nets are a classification of fishing method including beach seines, vessel operated seines like Danish and purse seines, and suripera. All seines are composed on a long net, which may have a bag in the center operated by two long ropes attached to the net’s ends. Seines can be operated from land or vessel to surround a certain area of water before being hauled to collect captured fish.

Species typically harvested: Demersal species such as cod

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.

Surrounding nets are a classification of fishing method including purse seines, lampara nets, and ring nets. All surrounding nets are large walls of netting used to surround aggregated fish.

Tanks are containment structures utilized in aquaculture, they include recirculating aquaculture systems (RAS) and simpler flow-through systems.

Trawls are cone-shaped nets that are pulled by a boat. The net is held open by two large boards attached to the net ends, or through pair trawling, when a net is pulled by two vessels. Trawls can operate throughout the water column. Midwater trawls do not contact the ocean floor and are used to target pelagic (open water dwelling) species. While bottom trawls are dragged across the ocean floor to harvest demersal (bottom dwelling) species.

Trolling 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

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.

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

Vertical lines consist of a fishing line which is 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.