黑料网

Gear; Aquatic species; Ghost fishing; Conservation

Introduction

The term “gillnet” refers to a wall of netting that is suspended vertically inside the water column with weights along the bottom and floats along the top, catching fish as they move around on fishing grounds. In theory, a gillnet is an imperceptible mesh panel that fish swim into without being aware of it [1]. Fish frequently become trapped in the mesh at the back of the gill cover and are unable to escape, hence the name “gillnet”. The gillnet fishery in the Northwest Atlantic may be traced back to the middle of the nineteenth century. In the beginning, cotton and other plant fibres were used to make gillnets. The invention of artificial elements and their software in fishing nets with within the Fifties and Sixties may be viewed into account a revolution in fishing gear technology [2]. Due to the large catch growth and nearly maintenance-free nature of the material, most natural fibre gillnet materials were replaced by artificial fibre in the Western world throughout the 1960s.

Structure and work

The United Nations’ Food and Agricultural Organization divides fishing gear into nine main categories plus other gears. Moreover, there are sub-kinds for each of the nine tool types [3]. Entangling nets and gillnets have been combined into a single tool kind comprising five sub-kinds and other kinds. The two primary sub-kinds of this category are set gillnets and driftnets. “Set gillnets” are defined as ground fish gillnets used inside the Northwest Atlantic.

Set gillnets are particularly stationary, tethered, or weighted to the lowest point. Japanese Canada and the northeaster United States refer to them as “gillnets” in the truest sense. A typical ground fish gillnet is 91 metres long and has a mesh size range of 140 to 203 mm [4]. For skates and monkfish, larger mesh sizes of more than 305 mm are employed. Gillnets are set at the lowest setting for types of floor fish, and in midwinter or very near the floor for pelagic species including salmon, herring, and tuna.

Driftnets are another name for drift gillnets. These nets don’t always hang at the lowest point; instead, they drift with the river and catch fish. Since it’s difficult to anchor floor gillnets in deep waters, driftnets can be tethered to a vessel that drifts with the currents [5]. Driftnets are frequently used in overfishing for oceanic species like salmon, tuna, and squid. Fisheries using high sea driftnets are clearly industrialised and extensive.

A trammel internet consists of three layers of nets. While the nets on the edges have huge mesh sizes, the middle internet has a reduced mesh length. Fish that swim through the mesh netting force the little mesh netting through the larger mesh netting, creating a pocket where the fish are trapped and held. Gillnets can be put onto stakes and used to create a wall or “fence” in shallow water and tidal environments. This is especially effective in rivers where strong currents can cause a gillnet’s normal geometry to be distorted.

One gillnet can be constructed by rigging together gillnet webbing of various mesh sizes to target specific species and sizes in mixed fisheries. You can combine gillnets with trammel nets to get the same result [6]. Combination gillnets are frequently used as sample tools for resource assessments and for analysing the selectivity of gillnets of different materials and designs.

Gillnets are made of a sheet of webbing that has been reinforced with the help of body ropes, along with floats and weights attached to widen the net in the vertical direction. Normally, many gillnets are connected together end to end to form a string of nets that is used for fishing as a single tool [7]. The stop gillnets have ropes attached to them to make retrieving easier. To become aware of the locations of both string stops, buoys and highflyers are used. The primary components are categorised inside the inset, demonstrating the artist’s effect on a rigid gillnet.

Discussion

The method that “causes the capture of the tools to have a unique composition to that of the population” within the region is the choice of fish with the aid of employing a tool. The quantitative assessment of this selection method, which is based entirely on organic samples collected in the field, is called selectivity. Processes, mechanisms, and analyses related to gillnet selectivity are examined [8]. The sigmoid and bell-shaped curves are the two main types of selectivity curves for fishing gears. The typical shape of a gillnet selectivity curve is bellshaped, and it may have or more peaks reflecting a particular strategy to capture. It is usual practise to determine gillnet selectivity using the modal length, the preferred variety, and the preferred parameter, which is the L0 to mesh length ratio. Gillnet selectivity is influenced by a number of factors, including mesh length, webbing type, putting ratio, and wire length.

The most important factor in determining the selectivity of gillnets is mesh length. For all species, larger meshes typically catch large fish. While studying young cod in Greenland waters, it was noted that more cod were being entangled through gilling as mesh length increased [9]. When mesh length increased from 33 to sixty six mm (1.3” to 2.6”), size distribution changed from having no obvious peaks to two peaks, then to a single height. While comparing gillnets with mesh sizes of 128 and 220 mm for Greenland halibut in the Barents Sea, the version period was 55 cm for the smaller mesh length and 66 cm for the larger mesh length. Mesh length regulation has been a common place control measure in many fisheries to reduce undersized fish. The minimum mesh length for the multispecies gillnet fishery in New England is 136 mm.

Webbing Substance Smaller twines typically have negative length selective properties due to elongations that occur when a fish pushes through the mesh and easier entanglements that result in a considerably greater length of fish becoming trapped. Because monofilament twines are more rigid than multifilament and multimonofilament twines, they have a stronger selecting ability for cod than both multifilament and multimonofilament nets [10]. Compared to multifilament and multimonofilament gillnets, which frequently tangle, monofilament gillnets catch a higher percentage of fish. Rate of Hanging Fish are more likely to become entangled in slackly-hung nets with low putting ratios than to be gilled, which results in poor length selectivity. When reading tilapia, Hamley found that the length ranged from 18 to 23 cm in a net that was hung tightly, but from 8 to 22 cm in a net that was hanging loosely [13]. Reduced Bycatch and Species Selection Gillnets have poor species selectivity and catch a wide range of species. The use of proper mesh sizes and fishing at designated sites are the main ways to reduce bycatch species and undersized fish. Cod and spiny dogfish catch was reduced when tie-down nets or nets with fewer meshes were used inside the vertical route, without reducing flounder catch. Purple king crab bycatch was reduced when gillnets were set up with Norsel traces that raised the net 0.5 metres above the seabed. Nevertheless, concentrated cod catch was also reduced.

Results

If the proper mesh length and netting materials are employed, gillnets typically catch larger fish than other types of gear. Gillnets offer higher length selectivity than other fishing gears, according to a number of comparative fishing studies. Gillnets stuck more large Greenland halibut when used concurrently at the west coast of Greenland than long-lines did [11]. Although though each gear caught fish with a similar height period of about 70 cm and a similar period range of 45 to 115 cm, long-lines caught a greater proportion of fish between 50 and 65 cm, and gillnets caught a greater proportion of fish between 65 and 85 cm. Cod are caught at the Flemish Cap using trawls, gillnets, and long lines by several fishing fleet sectors. According to equipment and country diagnoses, there are seven fleet sectors [12]. The average weight of fish caught through various fleet sectors and their share of the cod trap in 1991 has been established. The largest cod was caught by Portuguese gillnetters, averaging 2.5 kg, while the tiniest cod was caught by Spanish freezer trawlers, averaging 0.4 kg.

While comparing gillnets and trawls with mesh sizes ranging from 105 to 130 mm and focusing on Baltic cod, Lowry found that gillnets caught fish with height lengths 7 to 16 cm longer than fish caught with trawls using the same mesh length. Nedreaas and Huse compared #12/zero EZbaiter hook long-lines targeted at Greenland halibut in the Barents Sea off northern Norway with 220 mm mesh length gillnets with a 135 mm codend mesh length trawl [13]. They found that gillnet captures were typically made up of large, mature women, but trawl and long line catches had far fewer large, mature women. The average length of gillnet fish increased to 65.9 cm, compared to 59.6 cm for long linestuck fish and 50.1 cm for trawled fish. Similar findings were also found when three different types of equipment with a cod and haddock focus were compared.

Conclusion

The gillnet is a completely length-selective piece of fishing gear that works best with a small range of fish sizes. The mesh length and changes with the type of webbing material, wire length, and putting ratio are carefully related to size selectivity. The gillnet fisheries face two challenging conservation issues: species selectivity, which includes bycatch of marine mammals, sea birds, and turtles; and ghost fishing of lost fishing gear. There has been progress in research to lessen conservation challenges, but more work is required.

Conflict of Interest

None

Acknowledgement

None

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