Wild Capture & Farming Methods



Also called: Spearfishing

Habitat impact: Negligible

Bycatch: Negligible

Harpoon fishing is a highly specific fishing method, usually targeting large, high-value fish that live near the surface of the water. Harpoon fishers first spot fish in the water, then shoot them using a large spear attached to the boat by a line. Once harpooned, the fish is pulled in to the boat. Bycatch is extremely rare in these fisheries since the fishers are targeting specific fish; there is also negligible impact on the ocean floor as fishing takes place at the surface.

MSC certified North West Atlantic Canadian swordfish are caught using harpoons; you can watch a video of the fishermen at work here:


Dive fisheries

Also called: picking, gleaning, gathering

Habitat impact: Negligible

Bycatch: Negligible

Dive fishers SCUBA or freedive to retrieve species that are on rock walls or the sea floor. These fishers usually have minimal impact on the habitats in which they work, and there are very low levels of bycatch. Shellfish such as abalone and scallops can be caught using this method (scallops are also caught using dredges).

Check out a diver collecting scallops off Kangaroo Island:


Hook and Line

Also called: Handline, Pole and Line, rod and reel, jigging

Habitat impact: Negligible

Bycatch: Low

Hook and line fishing is the classic method we learn as kids – casting a line into the water and hooking a fish. Fishers use a line with hooks specifically targeted to the intended species. This method of fishing is selective because fishers can quickly remove unwanted catch from their hooks, reducing the amount of bycatch. This method also causes little habitat damage. Species caught using this method include squid and mid-sized fish, including mackerel, tuna, coral trout and MSC-certified Atlantic cod and haddock.

Check out how this fisher uses specific bait to jig for squid:

See how commercial fishers use pole and line for skipjack tuna in the Pacific:



Habitat damage: Negligible

Bycatch: Low

Trolling is similar to hook and line fishing, except that multiple lines are used. These lines are attached to long poles (“outriggers”) that keep them untangled. As the boat drives slowly through the water, fish are attracted to the moving hooks or bait. Heavy poles called downriggers can also be attached to the lines in the water to weight them to certain depths. Specific hooks, baits and depths are used to target species and reduce bycatch. Lines generally don’t touch the ocean floor, so habitat damage is minimal. Some salmon and MSC certified New Zealand albacore tuna are caught using trolling methods.

Check out a commercial albacore tuna troll in action:


Purse seine

Habitat Impact: Negligible

Bycatch: Moderate to high

A ‘seine’ is a type of net that is weighted on the bottom and buoyed with floats on top. Purse seining is so named because fishing boats circle the nets around a school of fish, and then draw the bottom of the net closed like the drawstrings on a purse, capturing the fish inside. Because purse seining occurs in the upper part of the water, there is little impact on ocean habitat. However, juvenile and under-sized fish may be caught in purse seines and other species such as dolphins can occasionally be caught as bycatch. Bycatch issues increase for some species when fishers use fish aggregating devices (FADs). The bycatch associated with some tuna fisheries includes turtles, sharks and cetaceans. Species caught using purse seines include Australian wild salmon, sardines and MSC certified PNA skipjack tuna.

See how Papua New Guinean fishers are purse-seining tuna without using FADs:


Pelagic gillnet

Also called: Mid-water gillnet

Habitat Impact: Low to moderate

Bycatch: Moderate to high

Gillnets are commonly used in small-scale and artisanal fisheries because they are simple to use and inexpensive, though are also used in larger fisheries. Pelagic gillnetting uses mesh nets set upright in the top and mid-depths of the water, and as the nets don’t touch the bottom, they have minimal impact on ocean habitats. The size of the mesh determines the size of fish caught, as individuals of target size get trapped in the net – their heads fit through the mesh but their larger bodies get caught up on their gill covers. While pelagic gillnet fisheries can catch threatened and vulnerable species such as seals, turtles and sharks in their nets, other gillnet fisheries are more responsible as they use correct mesh sizes for the fish they want to catch, and avoid areas where bycatch is likely.

Wild barramundi, trevally, and whiting are caught in gillnets in Australia.

See how traditional Arctic fishers use gillnets to catch salmon:



Habitat Impact: Low to moderate

Bycatch: Moderate to high

Driftnetting is a specific form of gillnetting where the nets are allowed to float freely in the water and are retrieved hours or even days later. They can be responsible for a high level of bycatch because of these unselective practices. There is also a chance that driftnets will be lost and become ghost nets, which can be a major problem. Ghost nets are very destructive, as their plastic mesh takes a very long time to break down and they continue to catch and kill fish and other marine life. While driftnetting is banned in many areas, including Australia, because of the potentially high impacts, it is still a very common method of fishing because it is so simple.


Mid-water trawl

Also called: Pelagic trawl

Habitat impact: Negligible

Bycatch: Moderate to high

Trawling consists of catching fish in a large, cone-shaped net that is pulled behind a boat. The net can be held open either by stiff poles or boards (‘otters’), or by being towed by two boats side-by-side.

Mid-water trawlers operate in the upper or middle parts of the ocean, so the nets don’t usually impact the sea floor. Bycatch can be an issue for some fisheries, including for marine mammals that can get caught in nets and drown. However, devices have been developed to reduce the impact of mid-water trawls on some species. For example, Seal Excluder Devices (SEDs) and Turtle Excluder Devices (TEDs) are fitted to nets, which act as escape hatches so that these species can escape the net.

The MSC certified Australia mackerel icefish is a mid-water trawl fishery and uses mitigation devices to reduce bycatch.


Pelagic longline

Also called: Drifting longline

Habitat impact: Negligible

Bycatch: Moderate to high

Longlines are made up of a series of shorter fishing lines with baited hooks on hanging vertically in the water. They are attached to a main line that’s anchored to the boat, and can stretch for kilometers with thousands of baited hooks hanging from the line.

Pelagic longlines are set in the upper or middle parts of the ocean, and have floats or weights attached along the main line to keep them at the surface or sink them to a certain depth. Since the lines don’t touch the sea floor, they have a minimal impact on ocean habitats. Longlines are predominantly used for targeting larger fish such as tuna and swordfish.

Pelagic longline fisheries can have bycatch issues. Seabirds, turtles, sharks and marine mammals are vulnerable to longlines as they are attracted to the bait or fish already on the hooks. Improvements in fishing technologies have helped pelagic longline fisheries reduce bycatch, such as specialised circle hooks to prevent animals from being hooked accidentally, and streamers or weights to keep lines out of reach of seabirds.

Mahi mahi and bigeye, albacore and yellowfin tuna from Australia are caught using longlines.

Check out how a Canadian longline operation improved their sustainability:


Pots and traps

Habitat impact: Negligible

Bycatch: Low

Pots and traps are wire or wooden cages that are set on the sea floor and often baited to attract animals inside. There are some concerns about localised habitat damage in areas with sensitive sea floor habitats, because the pots and traps can drag along the bottom. Additionally, the ropes that join the traps to floats on the surface of the water can entangle and drown marine mammals, turtles and seabirds. Advances in gear have helped reduce entanglements and bycatch. For example, modifications to pots used in the WA rock lobster fishery prevent Australian sea lions from entering pots and getting stuck.

MSC-certified Western Australia rock lobster and blue swimmer crab are targeted using pots and traps.

Take a look at the Australian rock lobster fishermen at work:


Danish seine

Habitat impact: Low

Bycatch: Moderate

Danish seining usually targets fish living near the ocean bottom (‘demersal’), or fish that are grouped in schools. In this method, a boat releases the seine net in a large circle to herd and trap fish, and then hauls in the catch. While Danish seines may touch or drag the sea floor, their impact is generally low. Bycatch can be an issue in some fisheries, as the nets can capture juvenile and non-commercial fish. Some MSC-certified Atlantic cod and haddock fisheries are fished using Danish seines.


Bottom longline

Also called: seafloor-set longline, demersal longline

Habitat impact: Low to moderate

Bycatch: Moderate

This method is similar to pelagic longlining, except that the long line is set on or close to the sea floor and the shorter hooked lines come off horizontally along the ocean floor. Benthic longlining targets bottom (‘benthic’) or near-bottom (‘demersal’) dwelling fish such as cod and flatfish. They may have some impact on the sea floor, depending on how sensitive the substrate is and how much the lines move and drag. Bycatch is an issue in many bottom longlining fisheries because non-target fish are attracted to the bait. Patagonian toothfish caught in Australia are mainly fished using bottom longlining.

Killer whale eating fish off longline:

Sperm whale eating fish off longline:


Bottom gillnet

Habitat impact: Moderate

Bycatch: Moderate to High

Bottom gillnets are similar to pelagic gillnets, except that the bottom of the net is set on the sea floor using weights. Bottom-dwelling fish swim through the net, and get tangled by their gill covers. Bycatch can be an issue with bottom gillnetting, as sharks and marine mammals can become entangled. Nets also disturb the sea floor, although effects are usually localised to the area where the gillnet is set.

Sharks can be caught with bottom gillnets.



Habitat impact: High

Bycatch: High

A dredge is a metal framed basket with a bottom of connected iron rings or wire netting called a chain belly. The lower edge of the frame has a raking bar, with or without teeth, depending upon the species targeted. The catch is lifted off the seabed or out of the sea by the raking (or teeth) bar and passes back into the basket or bag. Dredges are generally attached to a towing bar and one is operated from each side of the vessel simultaneously. As the fishing gear is in direct contact with the sea floor, delicate plants and animals, such as corals and sponges, inhabiting the sea floor can be damaged from dredging activity. The degree of impact depends on both the nature of the seafloor and the kind of animals in the dredged area.

Scallops and clams can be caught using dredges in Australia.

To see a dredge in action, click on this link:


Bottom Trawl

Also called: Seafloor trawl, demersal trawl

Habitat impact: High

Bycatch: High

Like dredging, bottom trawlers drag large nets across the sea floor to catch fish like cod and hake, and shellfish such as prawns. Similar to dredging, depending on where the fishery operates, bottom trawling can have the same issues with damaging marine habitat and bottom-dwelling animals. Bycatch can also be high with bottom trawling, as the nets are not selective in the species they capture; bycatch can make up more of the volume of catch than the target species. Creatures like deep water sharks, turtles, and many non-target demersal fish species are caught as bycatch in bottom trawl nets.

Ocean perch and blue warehou are bottom trawl-caught.

See a bottom trawl in action:

Demersal trawling is a form of bottom trawling that can be less destructive. Demersal fish live close to the bottom, so trawl nets move close to the sea floor to scoop them up. There are trawl fisheries that have minimised their impact on the environment, such as the Northern Prawn Fishery (NPF) that has reduced its bycatch by 50%. The NPF gained MSC certification in 2012.


In the best-case scenario, a fish farm would be clean, have good animal husbandry practices and have minimal impact on its surroundings. Fish produce waste, can harbour disease, escape, or farms can destroy habitat. Fish farms aiming to minimise their impacts on the environment by controlling these factors in order to produce quality products are operating in a more responsible way.

Below are descriptions of the various methods used to farm seafood.

Sea cage

Also called: Open net systems

Ask about: pollution, disease, escape risk, effects on environment


Fish are raised in pens, which are usually made of wire or plastic mesh and are open to the environment. The effects of open net pens on the environment depend greatly on the type of fish being farmed, the location of the fish farm and the management practices of the aquaculture operator.

Open net pens are handy for farmers, because they can use the flow of seawater to provide oxygen to fish and remove waste.

Risk factors to consider

With open pens the fish waste flows directly out into the ocean, and can be a source of pollution through nutrient overloading, which causes algal blooms. Aquaculture operations may also use chemicals, such as anti-foulants that stop marine growth on nets, and antibiotics to treat disease in fish. Chemicals used in the sea cage can flow out into surrounding water too.

The location of fish farms, called ‘siting’, is an important consideration in minimising the effects of pollution on wild habitats. A better aquaculture pen is one that is sited in an area of fast-moving water allowing the swift and widespread dispersal of waste. Farms that are sited in shallow areas where flow is slow cause build up on the sea floor and could result in killing local marine plants and animals.

Disease and parasites are also a concern with open net pens. Farmed fish are sometimes kept at higher densities than those at which wild fish naturally occur, and diseases can spread in these tight conditions. Left untreated, diseased farmed fish can, if they escape, pass parasites and bacteria onto the wild fish. Controlling disease in the farm and using techniques to reduce exposure of wild fish to farms is key to a responsibly managed fish farm.

Along with waste and disease, the fish themselves sometimes escape open net pens. Escape through or over the top of nets is a common occurrence in open net pens. If these fish are native to the area, they can join wild populations and may not have a huge impact on the local food web or habitat. But escapees that are non-native can turn into invasive pests, overtaking wild habitats and eating  native wildlife. For example, Pacific oysters, introduced to Australia for farming, rapidly began to displace native populations of Sydney rock oysters. Fish farms should carefully choose species and locations, and maintain their nets to minimise escape.

See how a Tasmanian open net pen salmon farming company feels about sustainability in their operation:


Closed-containment systems

Also called: Tanks, ponds

Ask about: pollution

One solution to issues with sea cages is using closed-containment systems, which fully enclose fish and shellfish. These systems can still have issues with pollution, so waste water needs to be treated and cleaned before being discharged on land or in the water.


Prawn ponds

Ask about: pollution, habitat destruction

The global demand for prawns and shrimp led to a huge increase in their farming, especially in South-east Asia. Unfortunately, the creation of ponds leads to the destruction of huge areas of mangrove forests along coastal communities. During the 1980s and 1990s, 35% of mangroves around the world were destroyed to make room for prawn ponds (World Bank, NACA, WWF and FAO. 2002. Shrimp Farming and the Environment. http://library.enaca.org/Shrimp/Publications/DraftSynthesisReport-21-June.pdf). Why does this matter? Mangroves are essential fish and crab nurseries, and provide vital habitat for other marine wildlife. They are also essential to protect coastal land from erosion. Additionally, prawn ponds produce a lot of waste that can pollute the coast, and harbour high levels of disease that can pass into native populations.

In Australia, most prawns are farmed in inland ponds, and 80% of this farming occurs adjacent to the Great Barrier Reef, with some concern over pollution and waste flowing into this sensitive area (Australian Prawn Farmers Association. 2013. Sustainable farming. http://www.apfa.com.au/environment/world-leaders-in-sustainable-prawn-farming/). These operations also require wild fish in the prawn feed, although effort is being directed into finding alternative feeds that reduce the need for wild-caught fish protein.

The sustainability of farmed prawns varies with country of origin and with the management in place. Make sure to ask about how they were grown when sourcing this seafood.

Farmed Australian prawns are green-listed in the AMCS Sustainable Seafood Guide, and are a better choice than farmed Asian prawns, which are red-listed.

Trays, Racks and Sticks

Ask about: nutrients

Shellfish are often grown on lines suspended in the water, or on trays fixed to the seafloor. Shellfish get their food by filtering it from the water and in some cases they can even improve water quality. Issues may arise when shellfish farms are so large that they remove too many nutrients from the water, taking food away from wild creatures, or high waste output unnaturally fertilises the surrounding water. Disease transfer from shellfish farms to wild populations can also be an issue.

In general, as long as the area is large enough with adequate flow bringing in nutrients, there is little effect on the environment.