TRAWLS, DREDGES, ETC. 207 



Dredges. Two kinds of naturalists' dredge were used, both supplied by the Marine 

 Biological Association and both of the double-sworded type. In working them the 

 usual procedure was adopted: one arm only was shackled to the warp and the other 

 was seized to it with several turns of trawl twine. If the dredge hitches, the seizing 

 parts, and by this means the chances of loss or damage are lessened. Both dredges 

 are galvanized, 4 ft. in length, 1 ft. in breadth, with arms 4I ft. long, and the only 

 difference between them is that one is of much heavier material than the other. The 

 lighter pattern proved much too weak for the very rough bottoms which were met and 

 after one or two trials its use was discontinued. In the heavier type the frame is 

 3 in. wide and bevelled from | to ij^ in. in thickness; the double bars which form the 

 arms are each f in. in diameter. The weight is about 140 lb. For work in the south 

 dredges of exceptional strength are required; bags, even of the heaviest netting, with 

 plenty of chafing material attached to the outside, were not infrequently torn away, 

 and we believe that they might more suitably be made of steel link. 



The conical dredge, with mouth 18 in. in diameter and a canvas bag, is designed to 

 bring up large samples of the bottom and for this purpose is a most efficient instrument. 

 Its use was adopted as a routine in the trawling survey made by the 'William Scoresby'. 

 This dredge has been described in detail by Borley.^ Small naturalists' dredges and 

 oyster dredges were also taken, the former for boat work. 



Fish Traps of various sizes were constructed for use from the ' Discovery ', and it was 

 hoped that good results would be obtained with them in comparatively deep water. 

 The largest was 10 ft. by 4 ft. by 4 ft., made of galvanized angle iron and netting; it 

 was only used once and was then unfortunately lost. It had been buoyed in deep 

 water off South Georgia, and with the onset of heavy weather two days elapsed before it 

 could be picked up. The buoy was discovered far away from its proper position and 

 the wire, though of over 2 tons breaking strain, was found to have parted. There is 

 little doubt that its loss was due to an iceberg having drifted across the position. It is 

 hoped that opportunity will be found for further experiments with large traps in deep 

 water. Off the north-east coast of South Georgia the bottom between depths of 300 

 and 2000 m. is exceedingly rough and traps appear to afford the only means of 

 obtaining those animals which can escape a dredge. Smaller traps were 4 ft. by 4 ft. by 

 2| ft., covered with ^ in. wire netting, and three different sizes of a cylindrical pattern, 

 covered with brass gauze. The latter were (i) 3 ft. by i ft. with J in. mesh, (ii) li ft. 

 by 6 in. with ^V in. mesh, and (iii) 9 in. by 3 in. with g'j- in. mesh. These were used 

 in shallow water, the largest sizes proving the most effective. They were generally 

 baited with whale meat. 



Nippers and Clamps. In trawling from the ' Discovery ' a nipper was used to transfer 

 the towing strain to a light rope stopper which broke at about 35 cwt., the arrangement 

 being that shown in Science of the Sear If the trawl hitches the stopper breaks, the 



^ Borley, Min. Agiic. Fisheries: Fishery Invest., ser. ii, iv, no. 6, p. 5, 1923. 



2 Science of the Sea, p. 276, fig. 195, London, 1912; 2nd ed., p. 315, fig. 193, Oxford, 1928. 



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