— 51 — 



which in reality have nothing to do with any actual alteration of the stock and landings, 

 play too great a part to permit of our drawing reliable conclusion^. In spite, however, 

 of these difficulties in connection witli the investigation of this problem, we can regard 

 the following as certain. 



The quantity in weight of older and larger plaice from about 45 cm. upwards has, 

 since the introduction of more intensive trawl fishing in the North Sea, decreased con- 

 siderably, not only relatively, but also absolutely. The relative decrease is shown by 

 the fact, that the percentage in weight of large plaice in the landings has more or less 

 regularly decreased, while that of the small fish has correspondingly increased. And 

 that an absolute decrease exists is evident from the fact that the percentual continues, 

 although the total quantity in weight of plaice landed has not decreased at all, but 

 even increased. This absolute decrease of the weight per cent must be equivalent to 

 an absolute reduction in the numbers of the largest and oldest plaice. As a matter of 

 fact, the experience of all the North Sea fishermen during the last 20 or 30 years 

 shows, that such plaice are, in comparison with former times, now rarely if ever caught. 

 Especially characteristic in this respect are the catches of the Danish plaice fishery. 

 Whereas formerly, before the introduction of intensive fishing by means of the "Snurre- 

 vaad" from larger vessels, i. e., in the /c's and 8o's, plaice weighing 20 to 45 kg. the 

 score, or of 50 cm. and upwards in length, made up an essential portion of the catch, 

 scarcely any such are caught now. This absolute decrease of the large plaice means, 

 with the same total weight of whole catch, besides a relative, also an absolute increase 

 in the numbers of the small plaice. The simple explanation of this is, that the loss 

 suffered by the fishery yield owing to the decrease of the large plaice is being compen- 

 sated by an increased capture of small plaice. That the average weight of the plaice in the 

 landings should also have decreased is easy to understand, and is also confirmed by ex- 

 perience in those places where corresponding catch statistics are kept, as for instance in 

 Denmark. There can be no doubt, that the decrease of the large plaice and increase of the 

 small in the landings, and the corresponding reduction in the average size of the plaice 

 are a direct result of the more intensive fishing and indicates, at the same time, an ac- 

 tual alteration in the composition of the plaice stock. The largest and oldest plaice — 

 or as Petersen expresses it, the old accumulated stock of same — have been fished 

 away, and are scarcely likely to be replaced, as long as the present intensive fishing 

 continues. 



2. Though it is an undoubted fact, that the composition of the original stock of 

 plaice is being permanently altered by the intensive fishing, it will yet be asked, on 

 the other hand, whether there are any ceitain signs that the size of the plaice stock 

 has simultaneously decreased in number and weight. In nearly every one of the 

 countries which fish the North Sea it has proved, that with the increased intensity of 

 the fishing, as evidenced by the increased number of fishing vessels, as well as their 

 increase in size, and the added catching power of the nets, the weight of plaice taken 

 per unit of catch — trawling hour, fishing day, cutter day — has on the whole con- 

 tinually decreased. This is however, in itself no strict proof that the density of the .shoals 

 of plaice has decreased owing to the more intensive character of the fishing; the phe- 

 nomenon could also be explained by the fact that in fishing a stock of plaice of a 

 certain constant size, the quantity of fish falling to each unit is inversely proportional 



7" 



