Fish trap

A fish trap is a trap used for catching fish and other aquatic animals of value. Fish traps include fishing weirs, cage traps, fish wheels and some fishing net rigs such as fyke nets.
The use of traps is culturally almost universal around the world and seems to have been independently invented many times. There are two main types of trap, a permanent or semi-permanent structure placed in a river or tidal area and bottle or pot trap that are usually, but not always baited to attract prey, and are periodically lifted out of the water.
A typical contemporary trap consists of a frame of thick steel wire in the shape of a heart, with chicken wire stretched around it. The mesh wraps around the frame and then tapers into the inside of the trap. Fishes that swim inside through this opening cannot get out, as the chicken wire opening bends back into its original narrowness. In earlier times, traps were constructed of wood and fibre. Fish traps contribute to the problems of marine debris and bycatch.

History

Traps are culturally almost universal and seem to have been independently invented many times. There are essentially two types of trap, a permanent or semi-permanent structure placed in a river or tidal area and bottle or pot trap that are usually, but not always baited to attract prey, and are periodically lifted out of the water.
The Mediterranean Sea, with an area of about of, is shaped according to the principle of a bottle trap. It is easy for fish from the Atlantic Ocean to swim into the Mediterranean through the narrow neck at Gibraltar, and difficult for them to find their way out. It has been described as "the largest fish trap in the world".
The prehistoric Yaghan people who inhabited the Tierra Del Fuego area constructed stonework in shallow inlets that would effectively confine fish at low tide levels. Some of this extant stonework survives at Bahia Wulaia at the Bahia Wulaia Dome Middens archaeological site.
In southern Italy, during the 17th century, a new fishing technique began to be used. The trabucco is an old fishing machine typical of the coast of Gargano protected as historical monuments by the homonym National Park. This giant trap, built in structural wood, is spread along the coast of southern Adriatic especially in the province of Foggia, in some areas of the Abruzzese coastlines and also in some parts of the coast of southern Tyrrhenian Sea.
The Stilbaai Tidal Fish Traps are ancient intertidal stonewall fish traps that occur in various spots on the Western Cape coast of South Africa from Gansbaai to Mosselbaai. The existing fish traps that can still be seen have been built during the past 300 years, some as recently as the latter part of the 20th century, whilst others could date as far back as 3,000 years.
Indigenous Australians were, prior to European colonization, most populous in Australia's better-watered areas such as the Murray-Darling river system of the south-east. Here, where water levels fluctuate seasonally, they constructed ingenious stone fish traps. Most have been completely or partially destroyed. The largest and best-known are those on the Barwon River at Brewarrina, New South Wales, which are at least partly preserved. The Brewarrina fish traps caught huge numbers of migratory native fish as the Barwon River rose in flood and then fell. In southern Victoria, such as at Budj Bim indigenous people created an elaborate system of canals, some more than 2 km long. The purpose of these canals was to attract and catch eels, a fish of short coastal rivers. The eels were caught by a variety of traps including stone walls constructed across canals with a net placed across an opening in the wall. Traps at different levels in the marsh came into operation as the water level rose and fell. The traps at Budj Bim are seen as a form of Indigenous aquaculture dating back at least 6,600 years, with the Muldoon traps system seen as the world's oldest stone walled fish trap, and longest used fish trap in the world.
Somewhat similar stone-wall traps were constructed by Native American Pit River people in north-eastern California. In South Australia, the Barngarla people of Eyre Peninsula combined the use of fish traps with singing "to call sharks and dolphins to chase the fish into the fish traps, where the Barngarla people would appear to spear and stone the fish."
A technique called dam fishing is used by the Baka pygmies. This involves the construction of a temporary dam resulting in a drop in the water levels downstream— allowing fish to be easily collected.
Also used in Chile, mainly in Chiloé, which were unusually abundant.

Types and methods

The manner in which fish traps are used depends on local conditions and the behaviour of the local fish. For example, a fish trap might be placed in shallow water near rocks where pikes like to lie. If placed correctly, traps can be very effective. It is usually not necessary to check the trap daily, since the fish remain alive inside the trap, relatively unhurt. Because of this, the trap also allows for the release of undersized fish as per fishing regulations.
Fish traps contribute to the problem of marine debris, unless they are made of biodegradable material, says a United Nations report. For example, fishers lost 31,600 crab traps in the Bristol Bay in a period of two years. Each year, fisheries in Chesapeake Bay lose or abandon 12 to 20 percent of their crab traps, according to a government report. These traps continue to trap animals. Fish traps can also trap protected species such as platypus in Australia.

Portable traps

These are usually in the shape of a pot or bottle.

Name	Image	Description
Atlantic cod pot		In 2017 research was reported on the suitability of using baited fishing pots for catching Atlantic cod. Stocks of this once popular commercial fish appear to be recovering after a major fishery collapse. The use of appropriately designed pots can have less environmental impact than other fishing strategies, but to be practical they need to catch their targets both efficiently and selectively.
Basic bottle trap		Bottle traps are also known as pot traps. This type of trap is portable, and is used to catch small fish and other small aquatic animals. It consists of a container shaped somewhat like a bottle, usually with an inverted funnel at the entrance. It can be constructed from a plastic bottle, or a glass jar or earthenware pot, or woven with wire or flax. The trap is lowered into the water on a line, where it is left either at the bottom, or suspended at some depth beneath the surface. Bait is usually, but not always used to lure the prey inside. Variants of this basic trap have been used from early times in countries around the world.
Bubu trap		Bubu are traditional fish traps in Southeast Asian countries such as Brunei, Malaysia, and the Philippines, specialized for catching fish in the uneven terrain of coral reefs. They are usually box-shaped or dome-shaped and are made from bamboo or rattan strips woven into hexagonal shapes. They vary in size and shape depending on the topography and current conditions of the locales they are used in. They have a wide opening at one end that narrows into an inverted funnel. They are used with or without baits and have weights or stones placed inside. They are placed on site then retrieved later. They are traditionally not marked with buoys, to avoid theft by other fishermen. Their locations are remembered via shoreline landmarks.
Crab trap		Different types of crab traps are used depending on regional preferences, the type of crab targeted and the underwater topography. Typically, they are constructed as wire cages, as shown in the image.
Eel trap		The New Zealand Māori wove intricate eel pots they called from the stems of climbing plants. At their best, these were works of art.
Fyke net		A fyke net is made from a bag-shaped net held open by hoops. These can be linked together in long chains, and are used to catch eels in rivers. Fyke nets equipped with wings and leaders are used in sheltered places in lakes where there is plenty of plant life. Hundreds of these nets can be connected into systems where it is not practical to build large fixed structures.
Katiska trap		A katiska is a portable fish trap used in Finland. It is a lightweight and made from chicken wire. The trap can either be collapsible or rigid, and is easily placed at any depth since it needs no anchoring. Katiska are commonly used in hobby fishing, since they catch only a small number of fish. The photo shows a fisherman checking a katiska.
Lobster pot		A lobster pot is a portable trap used to trap lobsters or crayfish. An opening permits the lobster to enter a tunnel of netting. Lobster pots are usually constructed in two parts from wire and wood. The lobster enters the first part, called the "chamber" or "kitchen", where there is bait. It then moves into the "parlour", where it is trapped. Lobster pots can hold several lobsters. They are usually dropped to the sea floor about a dozen at a time, and are marked by a buoy so they can be picked up later.
Octopus trap		In Japan, the Mediterranean, and other regions, an ancient variant is used to catch octopuses. They are usually heavy earthenware pots, and do not have an inverted funnel. These traps are left on the sea floor for days at a time. Octopuses enter and remain inside, using the pot as shelter and protection. No bait is used. When the pot is raised, the octopus will not normally try to escape. See also :ja:蛸壺 and piège à poulpe in Tunisia.
Soda bottle or glass jar trap		In Haikou, China, local people make bottle traps with small, glass jars. Local craftspeople produce a variant made from a two-litre soda bottle. This type has an inverted funnel made by cutting off the top of the bottle a few centimetres down the neck, and making vertical cuts downward. This produces tabs which are then pushed inward, producing the inverted funnel shape. A stone is attached to the side of the bottle, and several meters of line are provided. Numerous holes are drilled through the bottle to allow water to enter and escape. These are sold by the seaside for 6 yuan, along with a small bag of flour for bait.
Salambáw		Salambaw are traditional raft-operated lift nets widely used in the Philippines. It consists of a raft with a tower structure with a crane mechanism attached to two crossing spars with a large square-shaped net stretched in between. They are lowered and raised every few minutes to catch fish. They may use lights to attract fish at night. There are numerous variations of salambaw in the Philippines: a small hand-carried variant used to catch crabs is known as bintol; deep-water variants used to catch chambered nautilus is known as panak; stationary shore-based variants are known as tangkal; and variants operated from large outrigger boats are known as basnig.
Stickleback trap		The stickleback trap is a variant of the soda bottle trap.