12 JOHAN HJORT. M.-N. Kl. 



logical conditions in the sea beyond.« It is a fact,« he continues, »that 

 in the appearance of the food off our West Coast during the Summer 

 there are considerable differrences in different years. Some years the sea 

 during, it may be said, the entire Summer, has, in by the coast, been filled 

 with quantities of various kinds of food, while in other years it has almost 

 entirely vanished.« 



It therefore happens that as the Herring and its food is drifted far 

 from or near to the coast, the fishery will var}-, and just as the currents 

 may be presumed to vary from year to year, so will the fishing vary 

 from year to year. 



Until quite lately, however, the currents have been very little studied. 

 The Norwegian Northern Ocean Expedition, it is true, clearly described the 

 strong current which follows the Norwegian Coasts Furthermore, a number 

 of local investigations have been made along the shores in the various 

 fishery resorts, but these have not been able to yield any clear result, as 

 they were wanting in scientific methods and a leading plan of operations. 



It is certain that if one desires the truth as to the extent to which the 

 variations in the hydrographie conditions produce changes in the advance of 

 the fish, and thereby in the fisheries, one must both investigate that sea 

 whence the fish come, and that sea they wander to, and, besides this, the sea, 

 and the movements of the fish, must be studied at one and the same time, 

 and that under various conditions, both when the fishing is good and 

 when it is bad &c. &c., and these investigations must l)e extended from 

 the coast, seawards, as fast as possible, in order to learn all the conditions 

 which are present at a certain moment. 



Such a plan was first carried out by Swedish scientists, latterly under 

 the guidance of Professor 0. Pettersson-, Stockholm, and Mr. Engineer 

 G. Ekman, Gothenburg. i\s a field of operations they chose the Skage- 

 rak and Cattegat, where, as it is known, there is a rich Herring Fishery off 

 the Swedish shores of the Bohuslan. »The^ leading principle« says Pet- 

 tersson, »for investigations in the North Sea and the Baltic, regarded as 

 one entire hydrographical system, must be to distinguish between 

 the in and out-going layers.« The layers, which, proceeding from 

 the Baltic, run through the Cattegat and Skagerak outwards towards the 



1 See for instance Mohn's PI. XLIII (loc. cit.) and Den norske Nordhavsexpedition (The 

 Norwegian Northern Ocean Expedition). Tornoe: On the Saline Contents of the Water 

 in the Norwegian Northern Sea. PI. No. i. 



2 See, Otto Pettersson, A Review of Swedish Hj^drographic Research in the Baltic and 

 the North Seas; Scottish Geographical Magazine 1894. 



3 Loc. cit. July 1894, page 353. 



