Fisheries in Australia, and throughout the world, use a range of different techniques to catch seafood. Some of these have a much greater impact on marine environments than others, so it makes sense to support those fisheries that employ least-damaging fishing techniques. Here are some of the most common fishing techniques employed in Australia today and their pros and cons. We hope this information helps consumers to make informed choices when purchasing seafood by avoiding those products which have been taken with little regard for the environment. Also check out the Aquaculture Methods page, to learn how fish are farmed and raised.
Pole and Line Fishing
Dive Fisheries and Hand Collection
Pots and Traps
Dredging
Purse Seine
Pelagic Longlining
Demersal Longlining
Pelagic or Drifting Gillnet
Demersal Gillnet
Pelagic Trawling
Demersal Trawling
Ghost Fishing
Pole and Line Fishing
Pole and line fishing is a traditional method by which predatory fishes are captured one-by-one on hook and line. Schools are located and enticed into a feeding frenzy by maintaining a constant supply of live or dead baitfish to the water in a process known as ‘chumming’. Water may also be sprayed onto the sea surface, giving the effect of a fleeing bait school. Fisherman then present bare or baited hooks, or artificial lures, to the target fish which are hauled on board the vessel one at a time. Major pole and line fisheries target tuna species such as skipjack and albacore, however there are also numerous operations targeting tropical reef fishes.
Pole and line fishing is generally thought to have a minimal impact on habitat and fish stocks, however, localised depletions can occur. Bycatch rates are generally low, and unwanted fish can often be returned to the water quickly. There are some concerns that the use of baitfish for chumming can be unsustainable, and it is vital that the fisheries where those fish are sourced are rigorously managed. Ghost fishing through lost fishing gear is also an issue of concern.
Dive Fisheries and Hand Collection
Dive fisheries typically involve hand collection of the target species with the aid of a breathing device. Divers utilise either snorkelling equipment or systems that deliver compressed air from aboard the fishing vessel (hookah systems). Abalone and rock lobster are heavily targeted by commercial dive fisheries, whilst sea cucumber and sea urchins are becoming increasingly fished due to growing demand in both local and international markets. There are a range of collection methods depending on the target species and state regulations. Some common approaches may include gloved hand, leverage devices, hooks or tongs.
Dive fisheries are considered to have a negligible impact on the environment, as the collection method is highly selective of size and species. However, as a result of depth and accessibility limitations on divers, intensive hand collection can cause localised stock depletion, posing a significant problem in some areas.
Pots and Traps
Pots and traps can be used to catch a variety of fish and crustaceans. Mud crabs, blue swimmer crabs and rock lobster are species commonly targeted with these methods. The structure generally consists of a mesh body, with one way entrances leading into a baited enclosure. These techniques have a relatively low impact on habitat and are highly selective. Furthermore, unwanted catch can often be returned to the water unharmed.
The entanglement of sea turtles and marine mammals in marker ropes is a leading concern in pot and trap fisheries. Fortunately, the level of occurrence is generally minimal and often localised, allowing relevant management strategies to be implemented.
Dredging
Dredging is a technique primarily targeting bottom dwelling molluscs such as scallops and clams. The dredge comprises of a steel bar with rigid teeth attached to its base. As the dredge is towed behind the vessel, the catch is ploughed from the seafloor and collected in a mesh net or cage. Owing to the constant contact with the seafloor, dredging is amongst the most destructive methods of fishing in these habitats. Additionally, dredging can be highly unselective, with high levels of bottom dwelling fish and invertebrates often caught as bycatch.
Purse Seine
Purse seine fishing is a technique targeting pelagic (surface/open ocean) schooling fish such as tuna and mackerel. The vessel surrounds the school with netting before bringing the bottom together into a purse-like enclosure. As the targeted species generally congregate together at high density and in open water, purse seining can be highly selective and have little to no impact on marine habitat. In recent decades, reassessment of purse seining and its regulations has resulted in a greatly reduced bycatch of dolphins, however this occurrence remains the major concern in these fisheries.
Pelagic Longlining
Pelagic (surface/open ocean) longlining vessels deploy expansive lengths of baited hooks, whilst pursuing apex predators such as billfish, tuna and sharks. These lines are commonly between 10-100km long, and have thousands of baited hooks spaced consistently on branching lines (snoods).
Pelagic longlines remain suspended with buoys and pose minimal risk to marine habitats. The major concern in pelagic longline fisheries is that of bycatch. Seabirds such as albatross and petrels frequently drown after being caught diving for the baited hooks. Numerous strategies such as setting weighted lines deeper and/or at night and the use of bird scaring devices have aided in reducing seabird bycatch. The extensive lengths of fishing line also commonly cause the entanglement of sea turtles and marine mammals.
Demersal Longlining
Demersal (seafloor) longlining is a commercial method targeting bottom dwelling sharks and a vast range of scale-fish species. Demersal longlines are fixed along the seafloor using anchors, at depths as little as a few hundred metres down to many thousands of metres. In contrast to pelagic longlining, demersal operations often have shorter, more frequent branching lines (snoods) as well as shorter mainlines.
Compared with other bottom- fishing techniques, demersal longlining has a relatively low impact on marine habitas. As with most bottom fishing techniques, bycatch is a major concern in these fisheries, with many unsaleable shark and fish species being landed. As sharks and deep-sea species are commonly long-lived and slow growing, their removal can be highly detrimental at both species and ecosystem levels.
Pelagic or Drifting Gillnet
Pelagic (surface/open ocean) gillnets are systems of netting with highly specific mesh sizes. Gillnets as long as 2.5km, are placed vertically in the water column with the use of buoys and weights. These nets may be anchored or allowed to drift with prevailing currents, intercepting migrating sharks and fishes such as tuna and mackeral. Large fish become entangled in the net (commonly around the gills), whilst smaller fish are able to pass through the designated mesh size.
Gillnets are highly size selective and pose little risk to habitat when placed high in the water column. Due to the large expanses of netting, bycatch of turtles, diving seabirds and marine mammals is of great concern. Research using sound deterrents to diverge marine mammals from fishing areas is currently in progress.
Demersal Gillnet
Demersal (seafloor) gillnets are lengths of netting set in place vertically along the seabed, with the use of weights and buoys. They possess a predefined mesh size which results in the targeted fish being entangled in the net, whilst allowing smaller fish to swim straight through. Demersal gillnet fisheries target a range of shark and scale-fish species such as snapper and barramundi.
Gillnetting provides a highly size selective method of fishing, allowing undersized fish to avoid entanglement. They also have a relatively minimal impact on seafloor habitats when compared with other demersal fishing techniques. Conversely, their impact on non-target species can be significant, with marine mammals and unsaleable fish and shark species often being taken as bycatch.
Pelagic Trawling
Pelagic (surface/open ocean) trawling involves the towing of large nets behind one or more fishing vessels. Pelagic trawls rely on filtering enormous volumes of water in order to increase catch success. Net entrances may be several hundred metres wide and are held open with the use of floats on the upper edge and weights on the lower edge. Captured fish are funnelled into the back section of the net which is known as the cod-end. This method is commonly used to catch schooling pelagic species such as tuna and mackerel.
When targeting a single schooling species, pelagic trawling can be can be quite selective with minimal fish bycatch incurred. However, shark and marine mammal entanglement can be significant, particularly to dolphin pods pursuing shoaling fish. Seabird mortality is also a concern, as birds may collide with trawling cables or become entangled in the net whilst diving for captured fish.
Demersal Trawling
Demersal (seafloor) trawling is the general term for a number of trawling methods targeting bottom dwelling species. The main feature in all demersal trawling techniques is that the hauled net maintains contact with the seafloor as the vessel is underway. This is achieved by weighting the bottom edge of the net entrance, whilst floating the top edge with the use of buoys. These weights also assist in disturbing buried fish up into the water column. Demersal trawls are characteristically smaller than pelagic trawls, as bottom dwelling species generally remain close to the seafloor for food and refuge. Fish such as flathead, flounder and orange roughy are commonly targeted with the use of demersal trawls.
Demersal trawls have the potential to cause significant damage to the seafloor in fragile habitats. As the trawl is hauled along the bottom, marine flora as well as invertebrates such as sponges and corals may be ploughed from the bottom or crushed. In addition, demersal trawling has minimal selective potential, often resulting in high levels of bycatch.
Ghost Fishing
Ghost fishing is the term used to describe the capture or entanglement of organisms in lost or discarded fishing gear. Fishing equipment such as line and hooks, nets, pots and traps are often lost in waterways due to rough seas, unmaintained gear or snagging on the seafloor. Fisherman may also discard these items when they have become ineffective or faulty. This unmonitored fishing gear is then free to drift on ocean currents and tides, entangling and killing sea creatures indiscriminately.
Ghost fishing poses a significant threat to marine organisms. Pelagic (surface) ghost nets may drift around the oceans for years, entangling fish and marine mammals which may be passing by or attracted by the dead or struggling fish. Seabirds such as albatross may also become entangled when diving for trapped fish. Floating ghost nets also pose a risk of propeller entanglement for passing vessels.
Demersal (seafloor) ghost fishing is often from demersal gillnet fisheries, or pots and traps set by crustacean fisheries. These items affect ecosystems in ways comparable with pelagic ghost fishing. Ghost pots and traps catch the target animals, which then become bait for more individuals in an endless cycle. Some efforts have been made to retrieve lost fishing equipment, however, due to the drifting nature and unknown location of most equipment, attempts have been small scale and variable in success.
Source : http://goodfishbadfish.com.au/?page_id=31
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