1 he plaice, Pleuronectes platessa L., is never absent from the hauls made on the introduction 

 shallow sandy grounds of the North Sea extending eastwards from the 3° of longitude and 

 south of the 54° of latitude into the German Bight. It is one of the commonest inhabitants of 

 the West-Frisian "Wattenmeer" and of the estuarine region of the Dutch North Sea provinces. 



Differences occur, however, according to the region and time at which the plaice 

 are taken. They are larger further from the coast and on the same grounds, larger 

 plaice on the average are taken in spring than in summer. This depends upon the well- 

 known fact, that the plaice is a migratory fish which always moves further from the 

 coast as it grows older. 



This characteristic distribution was known to the fishermen of old and has also been 

 commented on by the older Dutch authors (van den Ende, Venema, Schlegel). 



Later Holt, Cunningham, Mc. Intosh, Petersen, Hjort, etc. have made the 

 same observation and studied the matter more in detail. For the Dutch region, Hoek 

 was the first to give some considerable examples. The smallest plaice were taken 

 quite close to the coast, whilst those taken about 60 Eng. miles off had the largest 

 average size. 



During the last two years, our investigations, which were devoted principally to the Material and 

 study of the habits and habitat of the plaice, have already led to a preliminary, yet, I 

 believe, a tolerably comprehensive insight into the pecuUar and for the practical fishery 

 highly important distribution of this fish on our coast. The material for these investig- 

 ations was collected by the research-steamer "Wodan" on twelve different cruises in the 

 North Sea and by smaller boats on numerous excursions in the neigbourhood of Helder 

 and in the Zuydersee. It has been proved therewith, that the investigation of some 

 fixed, well-chosen observation-stations formed an excellent method of studying the periodic 

 fluctuations in the occurrence of the fishes. 



In accordance with the directions given in the Christiania program, the method of 

 the investigations consisted in a complete as possible analysis of the entire catch of each 

 haul, which generally lasted two hours, regard being taken for the number, size, weight, 

 age and ripeness of the fish. Graphic representations, frequency-polygons, constructed 

 according to Petersen's method, were then employed to demonstrate the results. 



The measurements required for the determination of the average length have been 

 based on material consisting of more than twenty thousand plaice. This number is 

 quite sufficient for some of the questions considered here. It has thus appeared — as 

 already observed by earlier naturalists at other places — that the characteristic distribution 



methods 



