— II — 



district, and the habitat of larger plaice). By far the greatest and densest shoals of 

 young plaice are found in the inner, shallowest zone of the region, in Area A, especi- 

 ally in its sub-areas A 2, and As, and in the most landward parts of the somewhat 

 deeper Area B, especially Ba and B4. The density of the plaice as caught with the 

 ordinary otter trawl averages here 200 to 500 per hour, the maximum at certain 

 spots during the summer months being 2500, with a minimum in winter of from 10 to 

 20. This enormous difference in the density on the same grounds for summer and 

 winter is evidently due to the fact that the young plaice in winter hibernate hidden in 

 the ground, and are not turned up and taken by the trawl. 



3. Scientific hauls and Market-Samples as a means of displaying the 

 distribution of the plaice in the North Sea, and determining the com- 

 position of the plaice stock and of the plaice landings. 



All our conclusions as to the distribition ot the different age-classes of the plaice 

 and the composition, in point of number, of the stock of plaice in the sea and the 

 landings of plaice at the fishing ports, are naturally based on the investigation of single 

 samples taken from the great mass of fish. We distinguish between three kinds ot 

 samples: 



1. Scientific hauls, or stock-samples. 



2. Fishery catch-samples, and 

 J. Market-samples. 



The scientific hauls are samples of plaice, drawn up from the bottom by means 

 of scientific fishing implements of varying size and width of mesh, in such a way as to 

 ensure the capture of all those age- and size-classes which actually live together at a 

 given place. The scientific hauls are thus at the same time samples of the true 

 stock there found. 



The Fishery catch-samples are samples of plaice which are brought up with the 

 ordinary fishing implements in use. Certain small plaice, of under a certain average 

 size, determined by the width of mesh of the nets, are indeed caught by these imple- 

 ments, but escape again before they can be brought to the surface; these samples are 

 therefore, in all cases where such young plaice occur, useless as true samples of the 

 stock, and can only be regarded as sorted samples of same. 



Market-samples are samples of those plaice which are landed by the fishermen at 

 the ports, and brought to market. As the fishermen only rarely bring to market the 

 whole amount of the fish caught and brought up by their nets, but as a rule throw 

 overboard a more or less considerable number as unmarketable, these market-samples 

 are for the most part only sorted fishery catch-samples. Only on such fishing grounds 

 as for instance the deep sea areas D., where no escape of small plaice through the 

 meshes takes place, nor any deletion by the fishermen of a portion of the catch for 

 the sake of the market, can the market samples be considered as identical with the 

 catch-samples, and these again as identical with stock-samples. 



For general knowledge as to the biology and distribution of the plaice, the scientific 

 hauls or stock-samples are of the greatest importance; for the purely practical con- 



