On smooth ground trawling is commercially possible at all depths down to 300 fathoms. In few cases, however, is trawling carried on at greater depths than 200 fathoms.
Owing to the large amount of stores and repairs, etc., connected with the maintenance of a fleet of steam trawlers, most large owners maintain fairly elaborate premises in the neighbourhood of the fish dock. These premises generally consist of a net-making hall in which nets are made by women working with shuttles, a large bath of tar or tanning material below in which the net is soaked, also a wood yard and blacksmith’s shop, containing a steam hammer, a plumber’s shop, a boat-builder’s shop, a large store-room fitted with the necessary stores and spares.
During the war the steam trawlers were commandeered by the Government for use as patrol boats and mine sweepers. It is estimated that 10 per cent of our steam trawlers and drifters and their crews were lost during the war.
B.—Attachment of board to net. OB. Otter board. B. Iron brackets.
C. Chain to connect with warps. M. Metal strengthening pieces. M′. Iron shoe. HL. Head line. UW. Upper wing. LW. Lower wing. LL. Lacing connecting wings. GR. Ground rope. D. Balch of lower wing. SSS. Twine settings connecting balch to ground rope. A. Headline and lacing connected to board by shackle. B. Toe of ground rope connected to board by shackle.
C.—Bosom of a bobbin foot-rope for use on rough ground. AB. Balch line on head of belly and connecting with bosom of wings. SS. Wire seizings connecting balch to small intermediate bobbins, 6″ diameter (EE). Large bobbins up to 24″ diameter (FF).]
When steam trawling was first introduced it aroused general opposition, for there was not only the fear that their efficiency would lead to over-fishing in certain grounds, but it was said that the trawl, when dragged along the bottom, destroyed the eggs and killed the immature fish. The line fisherman found that steam trawling made it more difficult to catch demersal fish with baited hooks. He attributed this to the effect of over-fishing, but it is probable that contact with the otter trawls had made the fish rather more shy and, therefore, more difficult to catch by this method. It is unlikely that steam trawling will lead to serious over-fishing, except possibly amongst such sedentary fish as soles and plaice. It must be remembered that trawling is only commercially possible on comparatively smooth ground and down to depths of about 200 fathoms. Probably, therefore, the actual area trawled is only a small proportion of the total area that is inhabited by fish. It is possible, of course, that extensive and long continued trawling in a confined and relatively isolated area may scare the fish away; it is probable, however, that any area in which over-fishing appears to have produced temporary exhaustion will tend to recover automatically, since it would naturally be abandoned temporarily by the trawlers for more profitable fishing grounds. There is no doubt that trawling, unless the size of the mesh is carefully controlled, tends to remove large numbers of immature fish. Generally in ordinary beam trawling—cod, plaice, haddock, etc.—the mesh varies from 3 ins. diameter near the mouth of the net to about 1-1/4 ins. diameter at the cod end. If a much smaller mesh were used the resistance encountered by a full-sized net would be so great that it would be almost impossible to draw the net through the water. Smaller trawls of 1/2 in. mesh are used in shallow coastal waters for catching shrimps, small plaice and whiting. The size of mesh largely determines the size of fish that will be retained by the net, since the smaller, immature fish readily escape through the meshes. Of recent years the various fishery boards, with a view to preventing the catching of such small, immature fish, have increased the size of mesh that is to be used—particularly when trawling within the three mile limit, where the greatest proportion of immature fish is generally encountered. For steam trawlers working in deep water a 2-1/2 in. mesh is generally used, but within the three mile limit it is frequently increased from 3 to 3-1/2 ins.