If, in response to the invitation of the Bureau of the International Council for the 

 study of the sea I give here some observations on the periodic occurrence of the principal 

 fishes, based on the rich statistical material of the "Deutsche Seefischerei Verein", I am 

 nevertheless well- aware, that in so doing, I am raising an old and a difficult problem. 

 It has been well-known for long, that most of the fisheries are carried on at certain 

 periods and that the existence of such periods is almost always conditioned by the habits 

 of the fishes. If the fish occur in quantities worth catching, the fishermen as a rule 

 are soon on the spot and do not move until the catches no longer repay the costs of 

 the time and labour. Thus arises a fishery-period'. 



The occurrence of fixed period appears most clearly, when we consider the catch 

 of any single species. 



For hundreds of years, the great herring fishery in the North Sea has begun, 

 continued and ended at fixed times as if along a pre-arranged course. The Scandinavian 

 waters, however, present an even more classic example of the fishery-periods. In the 

 unique fjords and along the fringe of the mainland in front of them, seasonal periods of 

 a special kind occur in addition to the annual fluctuations. 



The Norwegian cod fisheries also furnish a classic example. Advanced posts 

 of the fishermen are already on the watch in December to see, if the cod shoals are 

 approaching the Lofotens. The telegraph sends the good news far through the land, 

 and the fishermen like the fish are quickly on the spot, and in the course of April they 

 both disappear again together. 



Similar examples might be given in quantity. I may further mention here, only the 

 mackerel, which is the object — apart from the important fishery in the Channel — 

 of a considerable drift-net fishery from the coast of Norfolk and Suffolk in the North 

 Sea in May, June, and further, in September and November ; but in August and September 

 on the other hand, it engages the attention of the Norwegian and Swedish fishermen in 

 the Skager Rak and north-western portion of the North Sea. 



In the neighbourhood of the German coast, the mackerel is a rarer guest; but it 

 appears here regularly also, though with fluctuations. It penetrates close to the coasts 

 of East Friesland. In igo2 it was comparatively abundant, and was taken in quantities 

 at Heligoland in the summer ol 1902. In 1903 it occurred only rarely, as in the years 

 preceding 1902 generally. 



The garfish (Belone vulgaris) is similar. Its fishery near the coasts lasts from 

 April to July. In 1902, it occurred here in but small quantities, but at the end of May 

 to the beginning of June, it gave rise to a rich catch at Föhr and Sylt. 



I) A fishing-period of quite a different kind is seen, e. g, in the oyster fishery; the limitation of the fishing 

 to the cold season of the year is conditioned by the circumstance, that the oyster must reach the consumer 

 living. This is difficult in tlie warm months, especially as the spawning period then affects the condition 

 of the animal. 



