150 STUDIES IN INSECT LIFE, ETC. 



which slowly set towards the east. From the 

 mouth of the Thames to the Skager Rak we 

 have traced the flow of these deeper waters during 

 the various seasons of the year. These currents 

 undoubtedly influence the distribution of the 

 bottom living fish, especially in their younger 

 and less active stages. The researches into these 

 bottom currents have been made by bottles 

 carefully weighted so that they trail along the 

 bottom of the sea floating, say, a foot or eighteen 

 inches off the ground. 



(13) Last, but not least, we have now an 

 absolute measure of the intensity of trawling 

 in the North Sea. The above-mentioned trail- 

 ing bottles have been refished to a really astound- 

 ing extent. Commercial trawlers have retaken 

 them at the rate of 54 per cent, per annum. 

 In one area 85 out of 390 of these bottles were 

 recovered in six weeks, in another 50 out of 

 270 were trawled in five weeks, representing 

 a local intensity of fishing, which, if continued, 

 would give us between 80 and 90 per cent, of 

 recaptures in a year. Marked fish yield closely 

 similar results. When we reflect on the chances 

 of their dying or losing their labels or being 

 overlooked and not returned to the Laboratory, 



