the larvae are symmetrical fishes contained in the upper water layers 

 Ydth the other planktono Soon thereafter they undergo a metamorphosis 

 whereby they obtain the typical flatfish forme This lasts about 6 

 to 7 weeks, after which there is a change in their mode of life© The 

 larvae move to the bottom, especially on shallow areas near the coast o 

 There, they find enough food and in the autumn have reached a length 

 of about 6.5 to 7o5 centimeters <> As they grow, they seek deeper water 

 and it may be said in general, that ihe length in centimeters is equal 

 to the depths in meters v/here they are found. Figure 10 shows a chart 

 from the plaice report compiled by BeinoJce (1913 a, b) for the 

 International Council for the Exploration of the Seao The chart shows 

 how plaice of various length groups are distributed over the North Sea. 

 It is based on English observations compiled by Mastermano It appears 

 that along the Belgian, Dutch, German and Danish coasts there is a 

 broad zone in which more than 50 percent of the plaice are smaller than 

 25 centimeters, and only 1 percent are larger than 35 centimeters. 

 There are also verj'- many small plaice in the regions B3 and B4o 

 Bttckmann (1933) estimates the number of plaice below 22 o5 centimeters 

 in the German Bight (except the Wadden Sea) to be 1,000 million to 

 1,600 million and thinks that half of this number appear off the Dutch 

 and Belgian coasts. The percentage of plaice of more than 26 centi- 

 meters in length increases with the distance from the coast and 

 northern latitudes. 



The plaice in the coastal zones do not remain in the same places 

 during the whole year but migrate periodically. The progress of this 

 migration was checked by Heincke and Mielck (1925) and B^ckmann (1927) o 

 It is shown in figure 11 <> This chart is a combination of several, 

 prepared by the authors, and shows the distribution of the piaice= 

 stock during various periods of the year along lines perpendicular to 

 the coast. It is clearly shown that the fish, which are concentrated 

 along the coast in spring, move further out to sea during the summer 

 months o There are few plaice in the coastal zones during the winter, 

 most of the young plaice having gone to deeper, warmer water. Many 

 others, especially the smallest, seem to bury themselves in the coastal 

 zone where the fishery cannot touch them. 



Besides this periodic migration and return, there is a gradual 

 movement of the larger plaice to deeper, more distant grounds© After 

 sexual maturity (usually for the first time after the fifth year) 

 they move to the Flemish Bight to spawn. 



Based on these facts, a commission of the Permanent International 

 Council for the Exploration of the Sea decided in 1921 to propose 

 the closing of the coastal zone for trawl fishing for the protection 

 of the no n -marketable plaice. This decree would be valid for all 

 steam and motor trawlers with a capacity of more than 50 horsepower. 

 These ships would not be allowed to fish during the whole year in a 

 zone between the coast and the 12 fathom curve from 52 N (Hook of 

 Holland) to 56° N (the so-called inner zone). During the first, 

 third and fourth quarter of the year fishing would be forbidden in 

 the area between the inner zone and the 15 fathom curve. That is, 

 from Heligoland to 56° N. Both zones are shown on the charts 



69 



