PETTERSSON- INTRODUCTORY — II 



In addition to these, there are the deeper regions of the Polar Basiii and the 

 Siberian and North American coastal banks, concerning which we have as yet no 

 exact data, also, the Greenland coastal banks, the area of which can be estimated 

 at about 700,000 □ km. If we omit the whale and seal fisheries, the entire fishery 

 is carried on only over the shallower coastal banks and plateaus which border the 

 deep region of the Norwegian Sea. We should commit an error, however, if we 

 left out of consideration, in studying the biological conditions of the food-fishes, 

 the deep region of the sea of 2,000,000 D km, where no fishing is carried on, 

 and limited our investigations to the 2,600,000 D km of the rich fishing banks and 

 shallower plateaus. Attempts have already been made in earlier years to gain a 

 fundamental insight into the problems, which have now been taken in hand by 

 the international work, partly by means of a general statistic of the fish caught 

 by the various countries in the North Sea, partly by means of the biological and 

 statistical investigation of a certain specially rich fish-area', which might serve as 

 an index of -the productivitj', as regards fish, of a tolerably large region of the sea. 



The reasons, why little progress has been made along these lines, become 

 evident when we consider the results of the hydrographical and biological investiga- 

 tions of recent years. 



The hydrographical investigations lead us to believe, that a close relation 

 exists between the occurrence of certain food-fishes in our seas and the distribution, 

 on the surface and in the depths, of the so-called Atlantic water (or more strictly, 

 of the oceanic water of over 35 °/oo salinity, coming from the more southerly regions 

 of the ocean over the submarine banks between Scotland and Iceland). 

 The Atlantic This Is tlic well-kuowu warm current of the North Atlantic Ocean, which 



was formerly believed to be an offshoot of the Gulf Stream. The international 

 investigations have shown, that in recent years the Atlantic water has entered the 

 Norwegian Sea almost exclusively between the F'seroes and Scotland over the 

 Wyville Thomson ridge. Another branch, which presses towards the north between 

 Iceland and the Faeroes, passes ordinarily not at all or but a little distance beyond 

 the crest of the submarine bank between these islands 2. 



The Atlantic water has a higher salinity {35'00%o to 35'6o°/oo) than the 

 remaining water of the Norwegian Sea with a salinity of somewhat under 35 %o, 

 but is specifically lighter than the latter owing to its higher temperature, and 

 thus streams into the Norwegian Sea as a surface-current. Owing to the influence 

 of the Earth's rotation, it is then bent to the east and sends a branch round the 

 Orkneys and Shetlands over the northern North Sea plateau into the depths of 

 the Norwegian Channel as far as to the Skager Rak. The trawl-fishery is carried 

 on in this water of Atlantic, origin over the whole northern North Sea plateau 

 (deeper than 80 m) as far as the Dogger Bank, and over the western and southern 

 Branches 01 the slope of thc Norwcglau Channel (Great Fisher Bank, Jutland Bank etc.). The 



Atlantic Stream 



I As for example, the Moray Firth, the Lofoten banks etc. 



- A similar hydrographical situation was also detected in these regions by the Danish Ingolf 

 Expedition in the summer months of 1896 and 1897. See: Den danske IngoUexpedition. I. 

 Hydrografie af M Knudsen. PI. I. Kobenhavn, 189g. 



