104 SEA FISHERIES 



number of steam trawlers was equivalent to 203,985 days' 

 fishing. In 1906 this figure had fallen to 164,321. In 

 short, the North Sea is being less fished because it shows 

 actual symptoms of depopulation. 



II 



Naturalists and fishermen both have sought for the 

 causes of this depopulation. These we will examine from 

 a critical point of view, in order to arrive at a correct and 

 practical conclusion. The causes are of two kinds : those 

 which arise in the course of nature and those which 

 arise from the practice of fishery; natural causes and 

 human causes. 



Let us take the natural causes first. We know that a 

 sudden change in the temperature or salinity of the water 

 leads to a corresponding change in the plankton, and 

 that the fish follow the plankton. In the course of ages 

 such changes must often have occurred. The feeding- 

 grounds of the fish were once there and are now here : 

 such is the simple formula of the phenomenon. It is 

 the same when the coastwise shoals undergo alteration 

 from the fact of new deposits or the alluvia of the rivers. 

 For example, the drift of the waters of the Rhone towards 

 the Golfe de Fos, a stretch of sea running from the Pointe 

 de Beauduc to Cap Couronne, deposits there every year 

 16 millions of cubic metres of mud and sand, which 

 render life impossible. When a bank of sardines or of 

 anchovies changes its ground for one a few miles away, 

 we hear always the same story : as the fishermen no 

 longer find the fish where they used, for them the fish 

 no longer exist. 



This is a flight, a change of residence, and not a 

 destruction. But we quickly come to the latter with the 

 appearance on the scene of voracious animals : porpoises, 



