passage has a valve or veil of netting called the “ fiapper, " which
only opens when the fish press against it on their way into the purse.
To understand clearly the facilities offered to the fish to enter the
pockets, it is necessary to remember that the trawl, when at work,
is towed along, with ]ust sufficient force to expand the net by the
resistance of the water. But this resistance directly acts only on
the interior of the body of the net between the pockets and then
on the purse; it does not at first expand the pockets, but tends rather
to flatten them, because they are virtually outside the general
cavity of the trawl and their openings face the father end of it.
The water, however, which has expanded the body of the net, then
passes under or through the fiapper or valve, and enters the purse,
which, being with a much smaller mesh than the rest of the net,
offers so much resistance that it cannot readily escape in that
direction; return currents are consequently formed along the sides,
and those currents o 'n the mouths of the pockets, which, as
before mentioned, are ffcing them; and the fish, in their endeavours
to escape, and finding these openings, follow the course of the pockets
until they can go no farther. The whole of the net is therefore
well expanded, but it is so by the pressure of the water in one direction
through the middle, and in the opposite direction at the sides
or pockets.
The dimensions of a full-sized beam trawl, such as has been described above are from 45 to 50 ft. along the beam and about 100 ft. in length. Trawls of practically all smaller sizes down to some 30 ft. are to be found, but except for shrimp trawls the large sizes predominate almost to the exclusion of smaller nets. The trawl-heads support the beam at about 3 or 312 ft. above the ground. The meshes of the net behind the beam (the square) are about 5 in. from knot to knot, when drawn out taut. In the batings, the part of the net in which the narrowing mostly occurs, they decrease gradually from 4 to about 3 in.; in cod end they are 212 in. In the hope of protecting the small fish from capture some local authorities enforce within their jurisdiction a minimum size of mesh for trawls, as for other nets. According to certain recent by-laws of the Lancashire and Western Sea Fisheries District Committee, for instance, every trawl used in their waters, except for the capture of shrimps and certain specified fish, must allow a square wooden gauge of a certain size to pass easily through its meshes when these are wet. The difficulties in the way of the efficacy of such restriction are that a mesh which would allow the escape of fish of but little value of one species might allow the escape of very valuable individuals of another kind; and that both local and national authorities alike have powers of Jurisdiction over such narrow strips of coastal water, that in the absence of an international agreement on the matter, the ground affected by the regulations is exceedingly small in comparison with the ground untouched. The same remarks apply to the similar regulations as to length of beam and circumference of nets.
Considerable skill is needed to work a beam trawl successfully. A knowledge of the ground and of the direction and time of the tide is essential; for the trawl is towed with the stream, a little faster than it is running, so that there may be just sufficient resistance to expand the net. The regulation of speed, seeing that beam trawls are worked only from sailing vessels, is a matter of difficulty; when, however, there is a sufficiency of wind much can be done by an adjustment of the length of tow rope. Lowering the trawl is also a matter of difficulty especially when wind and tide are contrary, as in that case the vessel tends to drift over the net: the apparatus is first got into position by paying out the rope attached to the trawl-heads in such proportions that the beam takes its proper position while close to the surface. These ropes, called “bridles,” are some 15 fathoms long: they meet and are shackled to the trawl warp, a manilla rope of 6 in. circumference, of which 150 fathoms are generally carried. The trawl being in proper position, the warp is allowed to run out and the trawl lowered to the bottom, the vessel slowly moving on meanwhile; usually the length of warp which is below the surface in towing is a few fathoms over three times the depth of water. The art of shooting the trawl lies in causing it to alight on its runners or shoes, with the net freely trailing behind: should the net be twisted, or the trawl alight on its beam, the trawl has been shot “ foul, " and must be hauled and shot again. While towing, an experienced fisherman can tell by pressing his hand firmly on the warp outside the ship's bulwark whether the progress of the trawl over the bottom is satisfactory, any irregular progress over rough ground revealing itself in the character of the vibration of the warp. The trawl usually remains on the bottom for a whole tide, or six hours, and will in this time have passed over some 15 m. of ground. Hauling, a most lengthy and laborious process if, carried out by hand-windlass, is in practically all modern fishing smacks carried out by a small steam capstan, the “steam man” as it is frequently called, a most efficient instrument with very compact engine housed under a small iron cover on the capstan’s top. When the trawl comes alongside the heavy beam is secured by its two heads, the net is hauled over the side bit by bit, by hand, until the cod end is reached, when a rope is passed round it above the bulging end which contains the catch, and then over a “ tackle "or pulley, and so the cod end is hoisted inboard. The knot of the codline is untied, and the fish, mixed with various invertebrate animals, star-fish and rooted forms (confounded in the one term “scruff”), falls to the deck.
A small trawl is often used from an open boat for shrimping. It closely resembles a beam trawl, but has no pockets. The usual dimensions of this net are about 15 ft. beam and 20 total length, of which about 4 ft. are taken by the cod end. The mesh is about half an inch square, but where no restrictions are enforced it decreases to a considerably smaller size as the cod end is approached. The beam when in use is about a foot and a half above the ground.
Shank nets are also similar to beam trawls in general shape, but differ in that the mouth is kept open by a rectangle of wood. Frequently the lower margin of the trawl's mouth is not in contact with the ground, being attached to a bar of wood which is fixed parallel to the bottom of the wooden rectangle and a few inches above it. A fish or prawn is thus disturbed by the bottom bar of the wood, and either jumps over it and below the net and so escapes, or over both bottom bar and middle bar into the net. The theory of the net's action is that the fish tends most frequently to take the former course, the crustacean the latter; and there is some evidence that this is partially realized in practice. Shank nets are sometimes worked from carts, when they are known as “ Trollopers.”
Owing to their fine netting and the very shallow water in which they work, shrimp trawls are exceedingly destructive to very small fish. Johnstone[1] has found for instance that in a two mile haul of a shrimp trawl on the Lancashire coast 567 small plaice are caught on an average, beside great numbers of whiting, dabs, soles and other fish. In most parts of the English coast regulations are in force as to the mesh, size of beam and length of haul of shrimp nets, and shrimpers working on the beach are ordered to sort their catch at the water's edge, returning as many young fish alive as possible. The proportion saved by these means is not known with accuracy; it is much greater in the case of short hauls than in longer ones. A shrimp trawl is usually kept down from half an hour to an hour, or when not subject to regulation rather longer. It is seldom towed for a longer period than 2 hours, the speed being somewhat under two miles per hour on an average, though subject to variation.
The beam trawl has been described at some length because its structure is somewhat more simple than that of the trawl now in more general use; the importance of the net as an engine of capture has undoubtedly declined greatly within the past generation. Some interesting figures collected by the British Board of Decay of Beam Trawling and rise of other Trawling from Steamers. Agriculture and Fisheries prove this incontestably. In 1893 the number of first-class British sailing trawlers was 2037, and their average net tonnage 57·4; in 1900 they numbered 925, with a net tonnage of 41·1, and from that year up to 1906 (the last year quoted in these returns) they never again reached a thousand in number or a tonnage of 40 tons net; on the other hand, there were in no one of the years quoted as few as 800 first-class sailing trawlers registered, nor did the average tonnage sink below 37, about which figure it remained constant. It is obvious therefore that about 1894 beam trawling began to decline, and that after a time this decline lost most of its power, the number of boats and size of boats having sunk to a condition in which they fulfilled a certain function, which for some years has remained fixed. The new factors which brought about this change went hand in hand. They were the invention of the otter trawl and the increasing use of steam in fishing vessels. The otter trawl has no rigid and heavy beam, but relies on the force with which it is towed through the water to keep it open, and it is a far more efficient instrument for the capture of all but small flat fish than the beam trawl. Owing to the second of these facts its employment inevitably spread, and owing to the first a sailing vessel needing at least a moderate breeze to give it the requisite speed for keeping a large net open was unsuitable for working it. Thus the introduction of the otter trawl undoubtedly hastened the replacement of sails by steam as motive power for the great fishing fleets. That the adoption of steam would have occurred in any case is almost certain. The conversion of drift-net fishing vessels from sail to steam has gone on rapidly, though no radical change of gear has taken place, and presumably the same would have occurred in the case of trawlers had the otter trawl never have introduced. There
- ↑ Johnstone, British Fisheries, p. 283 (London, 1905).
