FISHERY RESEARCH 325 



as the meshes of the nets used were rather large and the 

 smaller specimens could slip through with ease. Thus 

 we see how the coastal waters of Holland can form a nursery- 

 ground for a very great number of the stock of plaice in 

 the North Sea. This discovery is of great economic 

 importance. It is on the survival of these fish that the 

 future stock of large plaice depends. Immense damage is, 

 however, done on these grounds by long-shore fishermen 

 seeking other fish. So important an aspect has this assumed 

 that it has been seriously urged that at the time the young 

 plaice are there the grounds should be completely closed to 

 trawling fishing craft. 



From a size of four or five inches onwards we are 

 dependent on the statistics of the landings of fish for 

 information as to their general distribution. But while 

 these figures will give information as to their distribution 

 they tell us nothing of the movements of the fish or of 

 their subsequent growth. It is here that the system of 

 marking the plaice has proved invaluable. A small piece 

 of silver wire is pushed through the back of the fish and on 

 either end of it are attached small ebonite discs bearing a 

 number. The fish thus marked are then measured, and 

 their length, together with date and place of capture, is 

 inserted in a book opposite the number corresponding 

 with that on their discs. The fish are then liberated. 



Fishermen are notified that for each marked fish returned 

 to headquarters they will receive the market price of the 

 fish and a shilling for the disc. When a fish is recaptured 

 it is once more measured and, on comparing its length and 

 date and place of recapture with the original details for 

 the fish bearing that number, one can immediately tell 

 how much it has grown and how far it has travelled since 

 the day it was marked (Plate 115). 



In order to study the population of plaice in a large area 



