ii6 DISCOVERY REPORTS 



In oblique fishing, provided the ship is moving ahead slowly enough, practically the 

 only limit to the rate of haul is the bursting point of the net itself. By further 

 strengthening the gear therefore at all vulnerable points, and if necessary constructing 

 the meshing of the net of stronger material, it should be possible to haul at speeds up to 

 70 or 80 m. per min., giving a total fishing speed of about 3 knots. The main objection 

 to such a big increase in the oblique rate is that the time of fishing, already short 

 enough, would have to be still further reduced; at a rate of 70 m. per min., hauling 

 2000 m. which is the most that can be hauled without interfering unduly with the 

 vertical horizon, the fishing time would be barely half an hour. For this reason, then, 

 high-speed horizontal towing, if it could be accomplished, would be preferable. 

 Without much alteration of the existing gear, however, there seems to be little hope of 

 obtaining any marked improvement in the present horizontal rate. A much heavier 

 and stronger warp would certainly have to be used, and consequently a bigger and more 

 powerful winch, for the strain of towing such a large net at 3 knots, in view of the 

 enormous weight that would be required to keep it down, would probably be more than 

 tlie existing warp could stand. In the original horizontal experiments a 100 lb. sinker 

 was used at the end of the warp. If double that weight could be employed with safety 

 no doubt some increase in horizontal speed could be obtained without resorting to a 

 larger warp. At the same time various devices might be employed to improve the 

 catching power of the net itself. Non-return pockets might be provided as in the 

 commercial otter trawl, while, as already remarked, much of the existing obstruction 

 in the mouth could be avoided by the introduction of a heavier and more rigid frame. 

 It might reasonably be objected that any further increase in the fishing rate will 

 result in serious damage to the catch, but in view of the admirable condition of the 

 material that has recently been captured there seems to be little ground for anxiety on 

 this account. Slow fishing might well have a more detrimental effect, especially upon 

 the larger and more vigorous animals, which in their efforts to escape from a slow- 

 moving apparatus must no doubt suffer considerable damage through dashing them- 

 selves violently against the sides of the net. On the other hand in a net travelling at 

 high speed even the most active species must tend to be swept rapidly back to the 

 bucket, where, should they escape being stunned or killed outright, they must at least 

 be rendered immobile. 



Much of the recent experimental work could not have been undertaken without the 

 help of a reliable depth gauge. The instrument now in use, the improved deep-water 

 pattern described by Mackintosh, ^ has given excellent service throughout a long series 

 of hauls extending down to 3500 m. From the records obtained it appears that when a 

 large net is hauled rapidly from a slow-moving vessel it is inclined at first to move 

 almost horizontally through the water when the downward tendency of the warp and 

 net is more or less evenly balanced by the oblique upward force. As the haul progresses 

 the angle of ascent becomes gradually more accentuated, but it is only in the latter 

 stages shortly before closing is about to take place that the net begins to rise steeply. 



1 Mackintosh, N. A., and Ardley, R. A. B., 1936, loc. cit., p. 102. 



