Fishing nets are responsible for the largest share of Australia's fish catches, and are used in a wide variety of configurations and designs, depending on the species being targeted. The four main types of fishing gear that use netting are gillnets and entanglement nets, surrounding net, seine nets, and trawls. The main components of nets are described below.
Modern nets are typically constructed from synthetic fibres, such as monofilament nylon for gillnets, and multiple twisted or braided polymer filaments for seine and trawl nets.
The top edge of the net is attached to a rope called the headline, floatline or corkline. Floats are attached to the headline to provide buoyancy.
The bottom edge of the net is usually attached by hanging twine to a rope called the footrope or leadline. Weights or sinkers made of lead or other materials are attached to the footrope and spread the net vertically in the water. The type and number of floats and weights used depend on whether the net is to be positively or negatively buoyant (see below).
Gillnets and entanglement nets
Gillnets and entanglement nets consist of a panel (or panels) of net held vertically in the water column, either in contact with the seabed or suspended from the sea surface. The size of the mesh in the net determines the size range of the species caught, as smaller fish are able to swim through the mesh. The legal net length and mesh size are set by individual jurisdictions. Gillnets and entanglement nets are used in offshore and inshore waters, and in rivers and estuaries.
Fish are caught in gillnets or entanglement nets in one of three ways:
- gilled—the fish tries to swim through one or more meshes; if it cannot pass through, it becomes caught behind its gill covers as it tries to back out of the net.
- wedged—the fish is tightly held in the net around the body by one or more meshes
- tangled—the fish is caught in the net by some part of its body, such as protruding fins or spines.
Pelagic gillnets (also known as drifting gillnets or drift nets) are used in a number of jurisdictions including, Queensland and Northern Territory waters to target tropical sharks and mackerels. Pelagic gillnets are made up of individual net panels tied together, allowing easy removal or replacement of damaged sections. They are set in open water and can be set with the headline on the sea surface (positively buoyant) or suspended below the surface (negatively buoyant), with one end of the net often remaining attached to the vessel.
A common net
Photo: A pelagic gillnet
Demersal gillnets (also called bottom-set gillnets, shark nets, graball nets or mesh nets) are used to target Gummy Shark, in the Commonwealth-managed Gillnet, Hook and Trap Sector of the Southern and Eastern Scalefish and Shark Fishery. State-managed fisheries also use demersal gillnets to target finfish species. Demersal gillnets are similar to pelagic gillnets but are negatively buoyant and fish on the ocean floor. The boat does not remain attached to the gear, but may remain within a short distance of it.
A demersal gillnet
Coastal-, estuary- and river-set gillnets (also called swinger nets, mesh nets, running nets or offshore-set gillnets) are set in estuaries and adjacent to the coast. They are used throughout Australia, with the main target species in southern waters being mullet, bream, trevally, Luderick, Banded Morwong, warehou, flathead, Mulloway and King George Whiting. In Queensland, the Northern Territory and north-west Western Australia, Barramundi and Threadfin are the main target species. Estuary-set gillnets are set using small dinghies. The headline is tied to a tree or otherwise secured on the shore above the high-water mark. The dinghy is used to set the net across the river in a range of directions, depending on the tide and the species being targeted. Coastal-set and offshore-set gillnets are used throughout Australia. Offshore-set gillnets are set in at least 2 m of water, but coastal-set gillnets are usually anchored on the shoreline and may even be exposed at low tide, only catching fish as the tide rises.
Running nets are used for prawns. They are set in shallow water with a slight run-out current, between the boat and a channel. The prawns are worked along the net to the boat anchored on the end of the net, where they are collected in scoop nets. Swinger nets are used in South Australia to catch Mulloway around river mouths. They are set from the shore. One end of the net is placed in the water and allowed to drift out through the surf with the aid of the offshore 'rip' current, while the other end is held on the bank. The net swings around with the tide and is then hauled back onto the bank.
Ring nets (also called encircling gillnets, bull ringing, bunting nets, ring shots, power hauling, drain-off shots or round haul nets) are used in many parts of Australia to target species such as mullet, garfish, Australian Herring and whiting. They generally consist of a straight panel of netting (a pocket section may be incorporated) that is set around a school of fish sighted on the surface.
Typical ring net configuration
Surrounding nets take advantage of the shoaling behaviour of pelagic fish. The nets work by enclosing schools of fish within walls of netting that prevent the fish from escaping both outwards and downwards.
Purse-seine nets are used in the southern states of Australia to target schooling pelagic fish species, such as Australian Sardine, Jack Mackerel and Southern Bluefin Tuna. They are positively buoyant, with sufficient flotation to support the expected catch. The end of the net that is set first (the bunt) is heavily reinforced, as this is where the fish will be concentrated when the net is hauled. The footrope of the net has purse rings attached at regular intervals by rope or chain. A purse line runs through the rings; when the line is pulled, it effectively closes the bottom of the net.
A purse-seine net
Schools of fish are located by visual sighting, spotter aircraft or sonar. The fishing vessel travels around the school, setting the net, and the headline is then winched in so that both ends of the net are beside the vessel. The purse line is winched in from both ends, closing off the bottom of the net. The net is then pulled in towards the boat, and the catch is either pumped or lifted out in landing nets; alternatively, the entire net is lifted aboard. In the case of Southern Bluefin Tuna, the fish are transferred to towing cages and towed to sheltered waters closer to shore (for example, Port Lincoln in South Australia) over a period of days or weeks, after which they are transferred to aquaculture grow-out cages.
Seine nets usually have two long wings and a section that concentrates and retains the catch. Lengths of rope are added to the end of each of the wings. These ropes are negatively buoyant and extend the working area of the net while adding minimum drag to the hauling operation. The nets function on the principle that fish are reluctant to swim over a moving object in the water and instead try to swim in front of it. The fish are thus herded by the ropes and wing ends into the net.
Beach-seine nets (also called haul seines, pocket seines, baitfish seines, garfish seines, snapper seines, hauling seines, seines or estuary seines) are used Australia-wide to catch many species, including mullet, whiting, Australian Salmon, garfish, Tailor and bream. The net may have a loose section of netting acting as the bunt area for retaining fish, or may have a bag at one end of the net or in the centre. Beach-seine nets can be set around a sighted school of fish, or in an area where fish are known to congregate. The net is either set from a dinghy or can be walked out in shallow water, with the first length of rope being set perpendicular to the shore, the net set parallel to the shore, and the second rope set back to the shore. The ropes are then hauled onto the beach evenly, by hand, four-wheel drive vehicle or tractor, herding the fish into the net. Hauling continues until the net and fish are dragged onto the shore, with the fish are concentrated in the bag.
A beach-seine net
Danish-seining is the main form of boat seine used in Australia. It is used in New South Wales, Queensland, South Australia, Tasmania, Victoria and Western Australia to target a variety of species, including emperor, flathead, whiting and Redfish.
A Danish-seine net
Danish-seining gear is similar to a beach seine but is used on the continental shelf in depths up to 150 m to fish along the sea floor. The nets are negatively buoyant, and the lengths of rope used off each wing can be more than 40 times the length of the actual net. The principle of setting and hauling a Danish-seine is similar to that used for beach seining, but the process is undertaken from a boat rather than from the shore. The gear is set in a pear shape, with the net at the base of the pear and the ropes making up the sides. Retrieval of the net uses a combination of the forward movement of the vessel to close the net and hauling on the ropes using a powered winch.
Haul nets are used in South Australia, Tasmania and Victoria to catch Snapper, garfish, King George Whiting, Southern Calamari and bream. They are similar to a Danish-seine, with the net being positively or negatively buoyant, depending on the target species. The gear is deployed from small vessels in shallow water and is set in the same manner as a Danish-seine. The nets are predominantly deployed in waters shallower than 5 m, but may be deployed in waters deeper than 20 m when targeting Snapper. The ropes are short, and hauled either by hand or using mechanised winches while the vessel is stationary. Modified haul seines (ringing seines) are used predominantly in Corner Inlet, Victoria, where large tidal ranges require that the nets are usually hauled from within the boat. The nets have only one wing, and there are rings on the footrope through which a line is passed to purse up the catch.
River prawn seines (also called snigging seines) are used in New South Wales bays and estuaries to catch bay prawns and school prawns from small vessels. They are similar to Danish-seine, except that the net has a smaller mesh and the ropes are quite short. They are set and hauled in the same manner as a Danish-seine.
A river haul net
Lampara nets (also called ocean garfish haul nets) are used occasionally in Australia to catch pilchards (for example, Australian Sardines), Australian Anchovy and garfish. They are a more specialised type of surrounding net with wings (long, tapered panels of net added to each side of the bunt), giving the net a characteristic scoop shape. Lampara nets are mostly used at night with lights. The net is towed during the hauling process.
A lampara net
Trawl is one of the most widely used commercial fishing methods in Australia and internationally. Trawling is performed in many ways, in depths of water ranging from just a few metres to 1600 m. The design of trawl nets is more complex than the basic nets discussed above. Trawls are made up of components that perform specialised functions, as described below:
- Warps are wire ropes connecting the trawl boards to the vessel. They are stored on winch drums for ease of operation.
- Trawl boards (also called otter boards or trawl doors) keep the net open horizontally by acting as hydrodynamic kites. They also provide weight, which is required to keep the trawl at the desired depth of operation.
- Backstrops are short lengths of wire or chain that connect the trawl boards to the sweeps. Sweeps are used on demersal otter trawls to connect the backstrop to the bridle on each side of the net. Bridles connect the sweep on each side of the net to the headline and footrope on the wing ends of the net.
- Ground gear is a wire or chain that is attached to the footrope by short chain droppers. The ground gear may have several rubber or steel bobbins and spacers threaded along its length. The purpose of the ground gear is to reduce damage from snagging by lifting the footrope and net clear of the seabed.
- Body panels are the panels of net that make up the body of the trawl; they comprise upper and lower sections.
- The codend or bag is the last section of the net, where fish are collected and held during trawling operations. This area has the smallest mesh size, which determines the size of fish that the trawl will retain. The end of the codend is tied with a quick-release knot so that the fish can be easily emptied from the net.
The lazy line is sometimes used to pull the codend on board so that it can be emptied.
Trawl net configuration
Beam trawls (also called dredge nets, beam tide nets or push nets) are used in Queensland to catch school prawns and bay prawns. In northern Queensland and the Northern Territory, a beam trawl is sometimes used to sample the catch in demersal otter trawl prawn fisheries, both before the larger demersal otter trawl gear is set and during the trawl itself, to make sure the area being fished is still productive.
A beam trawl is simple in construction and can be used by small vessels, especially in restricted areas such as lakes and estuaries. It is constructed with two curved, steel end plates; the height of the end plates determines the vertical opening of the net. A straight steel bar that connects the tops of the end plates acts as a solid 'headline' and also determines the horizontal net opening. The top of the netting is attached to the beam, while the footrope is attached to the back of the end plates.
Demersal otter trawling for fish (also called stern trawling, bottom trawling, otter trawling or trawling) operates in south-eastern Australia, the south of Western Australia and the North West Shelf. A modified version (see semipelagic otter trawl, below) is used in some areas of the Northern Territory and Queensland. Australian trawl vessels also operate in Antarctic waters and on the high seas. Species taken in the southern fisheries include Blue Grenadier, Pink Ling, Silver Warehou, flathead and Redfish. In northern Australia, species taken include Snapper, emperor, rock cod and squid.
Demersal otter trawl gear
The trawl boards, sweeps, lower bridle and ground gear of demersal otter trawls remain in contact with the seabed during fishing. The net is held open horizontally by trawl boards being dragged along the seabed, spreading the sweeps, bridles and net wings. These herd the fish towards the net, where they are retained in the codend.
Demersal otter trawling for prawns (also called prawn trawling) takes place in all Australian states except Victoria and Tasmania. Tiger Prawns, Banana Prawns, King Prawns and Endeavour Prawns are the main species caught. Demersal otter trawls for prawns resemble a fish trawl, except that they do not employ groundgear, long sweeps, backstrops or long wing ends. They also generally have a smaller size mesh in the codend and body panels.
Prawns generally burrow into, or live on, the ocean floor. To reduce escapes below the footrope, a ground chain is used. This hangs below the footrope to disturb the prawns, causing them to jump up into the path of the oncoming net. In some fisheries, a tickler chain is also used, which is set in front of the ground chain. Similar trawl nets are used to target Saucer Scallops in Queensland and Western Australia, and Scampi in the Commonwealth North West Slope Trawl Fishery.
Demersal otter prawn trawl gear (left) and double rig configuration (right)
Long booms extending out from each side of the boat allow multiple rigs to be used. These rigs can be in a double, triple or quad net arrangement. The gear and rig configuration used often depends on the fisher's preference and the regulations imposed in a particular fishing area.
Semipelagic otter trawl (also called high-aspect semipelagic trawl or semi-demersal trawl) fishes close to the seabed, with only the trawl boards, wing end weights and chain droppers coming in contact with the seabed. This type of trawl net is commonly used to target finfish in the Northern Territory.
Midwater trawling is mainly used to target pelagic finfish such as Redbait, Jack Mackerel and Blue Mackerel in the Commonwealth Small Pelagic Fishery, and spawning Blue Grenadier in the Commonwealth Trawl Sector.
Midwater trawl nets resemble demersal trawl nets for fish, except that they are of a lighter construction and have a much larger mouth with short or no wings. The trawl boards are connected to the net via a long bridle and help to give the net its horizontal opening. Vertical opening of the net is achieved by flotation on the headline and weight on the footrope, as well as an additional weight on each lower bridle, close to where it connects to the footrope. The position of the net in the water column is controlled by the length of the warp and by varying the speed of the vessel.
Specific reports looking at different groupings
JurisdictionReports for each state or territory jurisdiction.
MolluscsMolluscs are invertebrate animals that includes the clams, calamari, squid, octopi and snails.
CrustaceansCrustaceans are a group of animals that include crabs, shrimps, prawns, lobsters and crayfish.
SharksSharks are a subgroup of cartilaginous fishes; usually large, fast swimming, fish-shaped predators.
FinfishFinfish are a vertebrate animals that have gills and live in water.