l895- ^0- 9- HYDR.-BIOL. STUDIES OF THE XORW. FISHERIES. i; 



dent on the state of the currents along the coast. Thus, the admirable 

 investigations of several years have proved that the approach of the 

 Herrings to the coast of Bohuslän during February, only occurs when the 

 Bank Waters flow in and fill those Fjords where the fishing takes place 

 as a rule. In Februar}-, as previoush* mentioned, the Bank Water is 

 warm in comparison to that of the Baltic Current. Its temperature is 

 about 4 ", and the saline contents great, amounting to 33 per 1000. 

 During three successive years it has happened that, so soon as this Bank 

 Water was forced back from the coast by the increasing current from the 

 Baltic, the Herring disappeared. The Baltic Current is then, in by the 

 Coast, at a very considerable depth, fresh and cold (temperatiu-e ranging 

 from 2° to — I "). Pettersson and Ekman thus conclude that the Her- 

 ri n^^ Fishery is directly assoàated zuith the presence of the Bank Water 

 on the coast. 



Besides adding greatly to hydrographical science, and throwing a 

 light on the Swedish fisheries in tlie Bohuslän, these investigations were 

 of excessively far reaching consequence in indicating an admirable method 

 of studying the natural conditions under which the various fisheries take 

 place. It appears especiall}- from the investigations, that it is of the 

 greatest importance to have large stretches of ocean thoroughly investi- 

 gated throughout, within a short space of time. Only by having an 

 accurate knowledge also of more distant waters could one conclude 

 whence the various lasers (currents) came, which, by a change in the 

 hydrographical conditions, arrive on a certain stretch of coast. 



One will understand how important it must be to obtain further 

 knowledge of these conditions. At the initiative of the Swedish scientists, 

 international cooperation was undertaken with the object of extending 

 the investigations at sea, from tlie Shetland Islands to the Baltic. 



The plan for this undertaking has been, partly, to collect materials 

 for charts of the North Sea at the most important seasons of the year, 

 which illustrate the saline contents of the surface water of the North Sea, 

 the Skagerak and Cattegat at a fixed period, and, partly, to study the 

 diffusion of the saline contents and temperature (of the various layers) of 

 the sea, by more local investigations. 



The materials for the surface charts have been collected by officers 

 of numerous steamers, who, during their voyages across the North Sea or 

 Skagerak, have made observations of the temperature and obtained 

 samples of the water even»* hour, or e^■er^' second hour. Most of tlie 

 samples have been collected for the Swedish scientists, but of those men- 

 tioned in the Tables of this work, various other steamship routes will also be 



