IMPOVERISHMENT OF THE GROUNDS 255 



value. ^ In order to obtain results of real value by 

 the application of such a method, a large trawl- 

 net fished for several hours must be employed, and 

 the results obtained can apply only to a com- 

 paratively limited area, and conclusions can only 

 be drawn from the averages yielded by a great 

 number of such trawling experiments spread over 

 several years, and even then the conclusions can 

 only be of the most general character. The useful 

 limits of the method are indicated by the results of 

 the series of trawling experiments of the Scottish 

 Fishery Board to which I have alluded above. 

 Only a small area, such as the Firth of Forth, could 

 successfully be investigated. To attempt to estimate 

 the productivity of such an area as the Irish Sea, or 

 even of one of the fishing banks in the North Sea, 

 by means of trawling experiments made by a single 

 vessel would probably be quite impracticable. 



The Statistical Evidence 



So far as it goes, then, the evidence deducible 

 from trawling experiments points to a distinct 



' Trawling statistics are sometimes corrected without due regard 

 being paid to the method of working of a trawl-net. See Sixteenth 

 Report of Inspectors of Fisheries for England and Wales, for 1902. 

 It is there attempted to compare the result of a haul of a trawl-net 

 made over (say) three miles of sea-bottom with one made over 

 one mile. This is the correction : A trawl will catch three 

 times as many fish in a three-miles drag as it will catch in a one- 

 mile drag. This is not the case, however, as any experienced 

 fisherman will know ; for as the net becomes full of fish, weeds, etc., it 

 becomes choked up and does not fish nearly so well as it did at first. 



