— 45 - 



As regards the composition of the stock, this can only be arrvied at by investiga- 

 tion of the so-called stock samples. These are catches made with such nets as are 

 furnished with sufficiently small meshes as to ensure the capture of every size of plaice 

 which is to be found at a certain spot. According to the experience gained from our 

 scientific catches with various kinds of nets, the ordinary trawl is here sufficient for the 

 purpose as far as regards the most of the central and all the northern areas of the North 

 Sea: in the southern coastal areas on the other hand, nets of narrower mesh are requ- 

 ired. Another question is, whether such stock samples, while satisfactory as regards 

 the nets, can be considered as representative of the local stock of the place of capture 

 at the time made; i. e. whether the various sizes are as thoroughly mixed in the sample 

 as on the sea floor. On this point we can unfortunately say nothing as yet. Moreover, 

 it must be borne in mind that the stock of plaice in the North Sea means the popu- 

 lation of the whole of the North Sea, and not only that of a certain part. The stock 

 of a certain ground (local stock) varies greatly according to the law of distribution of 

 the plaice, and differs also at different times. In order therefore, to obtain series of 

 measurements which can be regarded as more or less representative of the actual stock, 

 it is necessary to take numerous samples from all parts of the North Sea and at all 

 times of the year; these being, moreover, more numerous at such places and times, 

 as the density of the plaice is greater. In other words, the samples taken from the 

 different parts of the North Sea and at different times, must be proportional in size to 

 the local and periodical density of the plaice. This is a demand which it is unfortun- 

 ately impossible to satisfy at present: it could only be done by purely scientific catches, 

 methodically distributed throughout the whole of the North Sea, and this could only be 

 realised to a certain extent, for the bottom of the North Sea is in places so stony that 

 it impossible to use a trawl at all, although we cannot say that no plaice are to be 

 found there, especially since the results of line fishing prove the contrary. 



In the face of these extraordinary, and at present insurmountable difficulties, we 

 are obliged for the present to remain content with a knowledge of the composition of 

 the plaice stock in the North Sea which can only be considered as partially satisfactory, 

 and in particular, it is impossible, until we have carried out more thorough investigations 

 and employ better methods, to say anything with certainty as to the composition of 

 the younger portion of the stock of plaice, (up to 25 cm. in length). We must be 

 content to determine something about the older portion of the stock over 25 cm. And 

 here we can in the first place be certain, that the stock-, catch- and market-samples of 

 plaice of 25 cm. and upwards are equal in point of composition. The plaice landed in 

 England from the North Sea (market samples) are evidently catches which fulfil, for tlie 

 most part, the conditions i) that the catches be numerous, and taken from all parts of 

 the North Sea and at all times of the year, 2) that they be as far as possible propor- 

 tional to the density of the local and periodical stock of plaice — since tlie fishery, 

 pursued as a means of livelihood, would naturally fish the individual grounds in any 

 .sea as far as possible in proportion to the richness of the stock of fish. 



The Knglish market measurements will thus furnish us with the best possible know- 

 ledge at present obtainable as to the composition of the stock of plaice in the North 

 Sea, (or rather, in the southern and central parts thereof, as far as these can be fished 

 with the trawl). For several reasons however, the midsummer measurement series (i. e. 



