填空题
A The origins of gill net fishing cannot be traced with certainty, but it is clear that gill nets of one form or another have been in continuous use around the world for millennia. The principles and practice of gill netting are both so simple that it seems plausible that gill nets may well have been developed independently in different parts of the world. Certainly, no one nation or region can claim unambiguous credit for having initiated their use.
B There are various types of gill net. Drift gill nets (or driftnets) operate by gilling fish in the meshes of a sheet of netting. The netting is held more or less vertically in the water column by means of a buoyant floatline at the top of the net, and a leadline, to which weights are attached, at the bottom of the net. Nets rigged in this way may be used singly or, by joining them together serially, as a fleet of nets. Usually the floatline floats at the surface of the water, and the net hangs below it. Sometimes the floatline may be rigged in such a way that it floats some distance below the surface. The net then fishes a lower part of the water column. In such cases the net is partly suspended by additional buoys at the surface. In some sandy-bottomed areas, driftnets are even rigged to fish along the bottom of the seabed, for prawns especially.
C The net is left to fish passively, fish being caught when they swim into it and the meshes of the net become caught behind their gills. Driftnets may be attached at one end to the boat which is fishing them, or they may be left to drift flee of the boat and are recovered later.
D Driftnets are only one type of gill net. Set gill nets are also widely used in coastal waters and differ from drift gill nets in that they are fixed by means of anchors or stakes to prevent them from moving with the water. Driftnets, in contrast, are allowed to drift with the water currents or the wind.
E Driftnets are usually fished at night, as the meshes of the net are less visible to the fish. The type of material used in making the nets is also important in controlling the visibility of the net. In recent years monofilament nylon, which is a clear plastic, has been widely used, largely because it is usually more difficult to see, and is therefore more efficient at catching fish.
F Multifilament twines are also used in many driftnet fisheries, and have the advantage that they are less rigid than monofilament, which means that once a fish is gilled, it is less likely to be able to escape. They are also less bulky and easier to handle than monofilaments. To overcome their generally greater visibility underwater, multifilament yams are coloured in accordance with the environment in which they are being used.
G The vast majority of vessels using driftnets in the world are small boats, often used to supply family or village needs for pelagic fish. Often such gears have been used for generations, and the only modem improvement may be the use of nylon twines rather than cotton or hemp or other vegetable material. Nylon is, weight for weight, stronger than the natural fibres which were used traditionally. The greater strength of nylon compared with cotton or hemp for example, has meant that thinner twines can be used to catch fish of a given size, and this has improved the fishing power of the nets. Nylon is very often cheaper than a traditional alternative, although this is not the case everywhere, and this may have lead to an increase in the numbers of small vessels using driftnets. Furthermore, nylon is more durable than traditional materials, which also makes it more economical to use.
H On occasion, fish may not be caught simply by being gilled, but may rather become entangled in several meshes of the net. Sometimes nets may be rigged so that the sheet of netting is fixed to the floatline and leadline with plenty of slack to encourage entanglement; this is particularly so when awkwardly-shaped fish are targeted. The degree to which a net entangles rather than gills is determined by the "hanging ratio" of the net. This is the ratio of the length of the net when rigged, to the fully stretched length of the net (where the meshes are all closed). Typically for a gill net this ratio might be between 0.5 and 0.7, for example, which results in more or less rectangular mesh openings. The lower the hanging ratio is than this, the more the meshes of the net are distorted from a rectangular shape, and the more likely they are to entangle. If the hanging ratio is low enough the net may more correctly be described as a tangle net.
Questions 1-3
Label the diagram below.
For questions 1-3 choose ONE WORD ONLY from the passage for each answer.
Gill Net
Fishing
A The origins of gill net fishing cannot be traced with certainty, but it is clear that gill nets of one form or another have been in continuous use around the world for millennia. The principles and practice of gill netting are both so simple that it seems plausible that gill nets may well have been developed independently in different parts of the world. Certainly, no one nation or region can claim unambiguous credit for having initiated their use.
B There are various types of gill net. Drift gill nets (or driftnets) operate by gilling fish in the meshes of a sheet of netting. The netting is held more or less vertically in the water column by means of a buoyant floatline at the top of the net, and a leadline, to which weights are attached, at the bottom of the net. Nets rigged in this way may be used singly or, by joining them together serially, as a fleet of nets. Usually the floatline floats at the surface of the water, and the net hangs below it. Sometimes the floatline may be rigged in such a way that it floats some distance below the surface. The net then fishes a lower part of the water column. In such cases the net is partly suspended by additional buoys at the surface. In some sandy-bottomed areas, driftnets are even rigged to fish along the bottom of the seabed, for prawns especially.
C The net is left to fish passively, fish being caught when they swim into it and the meshes of the net become caught behind their gills. Driftnets may be attached at one end to the boat which is fishing them, or they may be left to drift flee of the boat and are recovered later.
D Driftnets are only one type of gill net. Set gill nets are also widely used in coastal waters and differ from drift gill nets in that they are fixed by means of anchors or stakes to prevent them from moving with the water. Driftnets, in contrast, are allowed to drift with the water currents or the wind.
E Driftnets are usually fished at night, as the meshes of the net are less visible to the fish. The type of material used in making the nets is also important in controlling the visibility of the net. In recent years monofilament nylon, which is a clear plastic, has been widely used, largely because it is usually more difficult to see, and is therefore more efficient at catching fish.
F Multifilament twines are also used in many driftnet fisheries, and have the advantage that they are less rigid than monofilament, which means that once a fish is gilled, it is less likely to be able to escape. They are also less bulky and easier to handle than monofilaments. To overcome their generally greater visibility underwater, multifilament yams are coloured in accordance with the environment in which they are being used.
G The vast majority of vessels using driftnets in the world are small boats, often used to supply family or village needs for pelagic fish. Often such gears have been used for generations, and the only modem improvement may be the use of nylon twines rather than cotton or hemp or other vegetable material. Nylon is, weight for weight, stronger than the natural fibres which were used traditionally. The greater strength of nylon compared with cotton or hemp for example, has meant that thinner twines can be used to catch fish of a given size, and this has improved the fishing power of the nets. Nylon is very often cheaper than a traditional alternative, although this is not the case everywhere, and this may have lead to an increase in the numbers of small vessels using driftnets. Furthermore, nylon is more durable than traditional materials, which also makes it more economical to use.
H On occasion, fish may not be caught simply by being gilled, but may rather become entangled in several meshes of the net. Sometimes nets may be rigged so that the sheet of netting is fixed to the floatline and leadline with plenty of slack to encourage entanglement; this is particularly so when awkwardly-shaped fish are targeted. The degree to which a net entangles rather than gills is determined by the "hanging ratio" of the net. This is the ratio of the length of the net when rigged, to the fully stretched length of the net (where the meshes are all closed). Typically for a gill net this ratio might be between 0.5 and 0.7, for example, which results in more or less rectangular mesh openings. The lower the hanging ratio is than this, the more the meshes of the net are distorted from a rectangular shape, and the more likely they are to entangle. If the hanging ratio is low enough the net may more correctly be described as a tangle net.
Questions 1-3
Label the diagram below.
For questions 1-3 choose ONE WORD ONLY from the passage for each answer.