I. 



1. 2. The general distribution of the plaice in the North Sea and its 

 various parts. The division of the North Sea into areas. 



The extensive investigations carried out by the International Commission for the 

 Investigation of the Sea with regard to the biology of the plaice, in particular as to its 

 age and growth, its reproduction, and the occurrence of the different stages from the 

 egg upwards, as well as its migrations, have given us very accurate knowledge as to its 

 distribution and extent, which information is as valuable as it is indispensable for arri- 

 ving at a correct solution of the plaice question. The following are the most essential 

 facts thus determined: 



The floating eggs of the plaice are spawned in the North Sea during the winter 

 months, chiefly in January and February, and in the deeper parts of this sea, from 20 

 to 30 meters, principally in the southern and south-western areas. From here the 

 pelagic fry move without exception towards the coast, and undergo there close in 

 to land, in quite shallow water of O to 5 meters depth, their metamorphosis to 

 the youngest bottom-stage, with distinct asymmetrical plaice form. From these flat 

 coastal zones, the true home of the quite young plaice fry in its first year of 

 life, the young plaice move, as they grow, outwards from the coast into the deeper 

 water until, having arrived at maturity (which takes place for the males on an 

 average at the close of the third, for females about the end of the fifth year) they 

 reach those districts of the open sea nearest their starting point where the necessary 

 conditions for spawning are found. This gradual seaward progress of the plaice, which 

 extends over a number of years, is carried out by stages, and during the summer, 

 being interrupted during the winter, when the young and still immature plaice hibernate 

 hidden in the ground, their feeding and their growth ceasing simultaneously. Besides 

 these regular periods of winter rest, the general seaward progress of the growing plaice 

 is also interrupted by shorter retreating movements directed towards the land, such as 

 that which for instance regularly takes place in the southern and south-eastern part of 

 the North Sea in the spring months, after the close of the hibernating period, the ob- 

 ject of which is in all probability to seek out better feeding grounds. 



Those plaice which have arrived at maturity move, as a rule, during the following 

 years, and with their further increasing size, still farther out to sea over the spawning 



