LARGE PLANKTON NETS 113 



been subjected when the net was being closed by the Nansen method. Some of the 

 animals, though taken below 1000 m., were brought to the surface alive and vigorous, 

 a circumstance for which the steady fishing of the forward open end of the net, through 

 controlling the collapsed portion behind, was doubtless largely responsible. 



There was, however, a serious objection to the internal method of closing when 

 applied so far down the net, for no matter how taut the throttling rope might be drawn 

 a narrow passage would always be left in the constriction through which, it was strongly 

 suspected, part of the catch in the fore part of the net was being carried by the pressure 

 of water back into the bucket behind. This objection was overcome by adopting a 

 closing arrangement which, while retaining the same throttling position 15 ft. away 

 from the bucket, was a compromise between the internal and Nansen methods. The 

 throttling rope, as before, was led inwards through the mouth of the net by way of 

 the fair-lead on the cross-wires, then out again through a small hole in the canvas band, 

 down through a series of rings sewn in one of the webbing supports, and so round the 

 outside of the net. The throttling rope, originally of li in. circumference manilla, was 

 now replaced by a 6 mm. diameter wire — not for the sake of its strength, but because it 

 renders so much more readily round the net than manilla. Thus rigged the net was paid 

 away to a depth of about 1000 m., closed immediately, and hauled rapidly to the surface. 

 The constriction was evidently a good one, blocking all access to the rear, for the whole 

 of the catch was confined to the fore part of the net and the bucket was empty. 



With the net in this rig a large number of closing hauls, both horizontal and oblique, 

 were conducted without hitch at all depths between 3500 and 400 m. The new closing 

 arrangement, however, simple as it was and thoroughly reliable mechanically, did not 

 meet with complete success, for although the condition of the material in the bucket 

 continued to maintain a consistently high standard, the actual quantity taken, as in the 

 early experiments, was still far from satisfactory. More than once during these opera- 

 tions the bucket came back practically empty, and never under any circumstances — 

 regardless that is to say of the speed, depth, or duration of the haul — was the catch 

 more than a fraction of what would normally be expected in such a large apparatus. 

 On the other hand the catch in the forward open section of the net was always 

 substantially large, generally from ten to twenty times greater than that in the bucket 

 behind. In view of the persistent failure to obtain satisfactory results a number of 

 tests were carried out in which the throttling rope was moved successively farther 

 away from the bucket, and as a result it was shown that the net was being throttled 

 too far aft, part of the catch which ought to have found its way to the cod-end 

 apparently being cut off to appear instead in the open section in front. The explanation 

 of this is not quite clear, but it is possible among other things that the animals these 

 nets are designed to capture, being big and powerful and exceedingly active swimmers, 

 may contrive for a time at least to remain far forward in the net, especially if it is being 

 towed slowly, with the result that if throttling takes place too far to the rear some of 

 them may never reach the bucket. 



In the arrangement finally adopted the net was throttled at a point half-way between 



